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A

ABC transport systems A type of active transport system that requires ATP as an energy source (ATP Binding-Cassette).

abscess  A localized collection of pus within a tissue.

acellular Not composed of cells, therefore not living.

acetyl-CoA Product of the transition reaction; a precursor metabolite used in fatty acid synthesis.

acid-fast staining A procedure used to stain organisms including members of the genus Mycobacterium that do not readily take up stains. Once stained, mycobacterial cells resist decolorization with an acidic solution of alcohol.

acidic amino acids Amino acids with more acid (-COOH) than amino (-NH₂) groups.

acidophiles Organisms that grow optimally at a pH below 5.5.

acquired resistance Development of antimicrobial resistance in a previously sensitive organism; occurs through spontaneous mutation or acquisition of new genetic information

acridine orange A fluorescent dye that binds DNA and can be used to determine the total number of microorganisms in a sample.

actin Polymer that makes up microfilaments of eukaryotic cells; it can rapidly assemble and subsequently disassemble to cause motion.

actinomycetes  Filamentous bacteria, many are valuable in the production of antibiotics.

activated (immune) T lymphocytes T cells activated by exposure to antigen.

activated macrophages  Macrophages stimulated by cytokines to enlarge and become metabolically active, with greatly increased capability to kill and degrade intracellular organisms and materials.

activated sludge method  A method of sewage treatment in which wastes are degraded by complex populations of aerobic microorganisms.

activation energy Initial energy required to break a chemical bond

activator-binding site Site that precedes an ineffective promoter; binding of an activator to this site enhances the ability of RNA polymerase to initiate transcription at that promoter.

active immunity Protective immunity produced by an individual in response to an antigenic stimulus.

active site Site on an enzyme molecule to which substrate binds; also known as the catalytic site.

active transport  Energy-requiring process by which molecules are carried across cell boundaries; can accumulate compounds against a concentration gradient.

acute infections Infections in which the symptoms and signs have a rapid onset and are usually severe, often with fever, but short-lived.

acute phase response Changes in the blood that occur early during an infection, with the production of acute phase proteins and cells that contribute to the inflammatory response.

acylated homoserine lactone (AHL) Small molecules that can move freely in and out of a cell; provides cells with a mechanism of assessing cell density (quorum sensing).

ADCC (antibody-dependent cellular cytotoxicity)  Nonspecific killing of target cells by cells such as macrophages, granulocytes or natural killer cells, that contact the target via their Fc receptors binding to Fc of antibodies on the target.

adenosine diphosphate (ADP) The acceptor of free energy in a cell; that energy is used to add a inorganic phosphate (P_i) to ADP, generating ATP.

adenosine triphosphate (ATP) The energy currency of a cell, serving as the ready and immediate donor of free energy.

adherence A necessary first step in colonization and infection, in which the pathogen attaches to host cells to avoid being removed from the body.

adjuvant  Substance that increases the immune response to antigen.

ADP  Abbreviation for adenosine diphosphate.

adsorption  Attachment of one substance to the surface of another.

aerobic respiration Metabolic process in which electrons are transferred from the electron transport chain to molecular oxygen (O₂).

aerosol  Material dispersed into the air as a fine mist.

aerotaxis Movement towards, or away from molecular oxygen.

aerotolerant anaerobes Organisms that can grow in the presence of O₂ but do not use it to generate energy; also called obligate fermenters.

aflatoxin Potent toxin made by species of Aspergillus; may contaminate peanuts and other grains.

agar Polysaccharide extracted from marine algae; used to solidify microbiological media.

agar slant. Microbiological medium that has been solidified with agar and stored in a tube that was held at a shallow angle as the medium solidified, creating a larger surface area.

agarose Highly purified form of agar used in gel electrophoresis.

agglutination Clumping together of cells or particles.

AIDS Acquired immunodeficiency syndrome.

AIDS-related complex (ARC) A group of symptoms, fever, fatigue, diarrhea, and weight loss, that herald the onset of AIDS

alga  (pl. algae) A primitive photosynthetic eukaryotic organism.

alkaliphiles Organisms that grow optimally at a pH above 8.5.

alkyl group Short chain or single carbon atom such as a methyl group (-CH₃).

alkylating agent Chemical that adds alkyl groups, short chains of carbon atoms to purines and pyrimidines; promotes mutations.

allele One form of a gene.

allergen  Antigen that causes an allergy.

allergic rhinitis Hay fever; sneezing, runny nose, teary eyes resulting from exposure of a sensitized person to inhaled antigen; an IgE-mediated allergic reaction.

allergy  Hypersensitivity, especially of the IgE-mediated type.

allograft Organ or tissue graft transplanted between genetically nonidentical members of the same species.

allosteric site Site on an allosteric enzyme that binds an effector molecule; binding alters the activity of the enzyme.

alpha (a ) hemolysis Type of hemolysis observed on blood agar characterized by zone of greenish clearing around the colonies.

alternative pathway Pathway of complement activation nonspecifically initiated by bacterial substances such as endotoxin and polysaccharides.

amalgam Mixture of mercury with other metals to form a paste that hardens; used to fill cavities in teeth.

amino (or N terminal) The end of the protein molecule that has an unbonded –NH₂ group.

amino acids Subunits of a protein molecule.

aminoglycosides Group of antimicrobial medications that interferes with protein synthesis.

ammonification  The reactions that result in the release of ammonia (NH₃) from organic nitrogen-containing molecules.

amphibolic pathways Metabolic pathways that play roles in both catabolism and anabolism.

amylases Enzymes that digest starches.

anabolism Cellular processes that use the energy stored in ATP to synthesize and assemble subunits such as amino acids; synonymous with biosynthesis.

anaerobes Organisms that grow in the absence of molecular oxygen.

anaerobic Contains no molecular oxygen (O₂).

anaerobic respiration. Metabolic process in which electrons are transferred from the electron transport chain to an inorganic terminal electron acceptor other than O₂.

analytical study An epidemiological study done to identify specific risk factors associated with developing a certain disease.

anamnestic response (memory response, secondary response) Enhanced immunological response to a second or subsequent dose of antigen.

anaphylaxis  Generalized hypersensitive reaction to an allergen that can cause a profound drop in blood pressure.

anion  Negatively charged ion.

anoxic Devoid of O₂

anoxygenic phototrophs Photosynthetic bacteria that use hydrogen sulfide or organic compounds rather than water as a source of electrons for reducing power; they do not generate O₂.

antagonistic In antimicrobial therapy, a combination of antimicrobial medications in which the action of one interferes with the action of the other.

antenna complex Complex in photosynthetic organisms composed of hundreds of light-gathering pigments; acts as a funnel, capturing light energy and transferring it to reaction-center chlorophyll.

antibacterial drug Chemical used to treat bacterial infections.

antibiogram Antibiotic susceptibility pattern; used to distinguish different strains.

antibiotic Chemical produced by certain molds and bacteria that kills or inhibits the growth of other microorganisms.

antibiotic-associated colitis Intestinal disease caused by overgrowth of toxin-producing strains of Clostridium difficile; typically, only occurs when a person is taking antimicrobial medications.

antibody Immunoglobulin protein produced by the body in response to a substance and that reacts specifically with that substance.

anticodon Sequence of three nucleotides of a tRNA molecule complementary to a particular codon in mRNA.

antigen Molecule that reacts specifically with an antibody or immune lymphocyte.

antigen presentation  Process in which macrophages, dendritic cells or B cells ingest and partially degrade antigens which then appear on the cell surface in a form that can react with CD-4 T lymphocytes

antigen-binding sites  Hypervariable regions at the ends of the two arms of an antibody molecule that recognize specific antigen; there are two identical antigen-binding sites on each monomer of antibody.

antigenic determinant Part of an antigen molecule that binds the specific antibody; an epitope.

antigenic drift Slight changes that occur in the antigens of a virus; specific antibodies made to the antigen before the change occurred are only partially effective.

antigenic shift Major changes that can occur in the antigen of a virus.

antigenic variation Routine alteration by an organism in the characteristics of certain of its surface proteins

antimicrobial drug Chemical used to treat microbial infections; also called an antimicrobial.

antiparallel Term used to describe opposing orientations of the two strands of DNA in the double helix; one strand is oriented in the 5’ to 3’ direction and its complement is oriented in the 3’ to 5’direction.

antiporter Transport system that exchanges the location of one molecule or ion for another.

antisense strand Complement to the sense (or plus) strand of RNA. Also called the minus (-) strand.

antiseptic A disinfectant that is non-toxic enough to be used on skin.

aplastic anemia Potentially lethal condition in which the body is unable to make blood cells.

apoptosis Programmed cell death, with enzymatic degradation of DNA.

arbovirus Arthropod-borne virus. One of a large group of RNA viruses carried by insects and mites that act as biological vectors.

Archaea Domain name for single-celled prokaryotes that usually grow in extreme environments.

archaebacteria A major group of prokaryotes that differ in many respects from true bacteria and usually grow in extreme environments.

arteriosclerosis Condition characterized by thickening and loss of elasticity of the walls of arteries; "hardening of the arteries".

arthropod Classification grouping of invertebrate animals that includes insects, ticks, lice and mites.

Arthus reaction Hypersensitivity reaction caused by immune complexes and neutrophils

artificial wetland method Method of sewage treatment in which sewage is channeled into successive ponds where both aerobic and anaerobic stabilization occurs.

aseptic technique Use of specific methods and sterile materials to exclude contaminating microorganisms from an environment.

aseptic  Free of infectious agents; sterile.

asexual  Reproduction not preceded by the union of cells or genetic exchange.

A-site (aminoacyl site) Site on the ribosome to which tRNAs enter to donate their amino acid; acceptor site.

asthma Immediate respiratory allergy resulting from mediator release from mast cells in the lower airways

astrobiology Study of life in the universe.

atomic force microscope Type of scanning probe microscope that has a tip mounted so it can bend in response to the slightest force between the tip and the sample.

ATP synthase Protein complex that harvests the energy of a proton motive force to synthesize ATP.

ATP Abbreviation for adenosine triphosphate.

attack rate Proportional number of cases developing in a population exposed to an infectious agent.

auramine Fluorescent dye that binds to a compound found only in the cells wall of members of the genus Mycobacterium.

autoclave  Device employing steam under pressure used for sterilizing materials that are stable to heat and moisture.

autoimmune disease Disease produced as a result of an immune reaction against one's own tissues.

autolyze To spontaneously disintegrate as a result of enzymes within the cell

autoradiography The use of film to detect a radioactive molecule.

autotroph  Organism that can use CO₂ as its main source of carbon.

auxotroph Mutant of a microorganism that requires an organic growth factor.

avirulent  Lacking disease-causing attributes, such as a capsule.

a_w  Abbreviation for water activity.

axial filaments  Organ of motility found in spirochetes.

azoles Large family of chemically synthesized medications, some of which have antifungal activity.

B

B Cells Cells of the immune system that secrete antibody

bacillus (plural: bacilli) Cylindrical-shaped bacterium; also referred to as a rod.

bacitracin Antimicrobial medication that inhibits cell wall biosynthesis by interfering with the transport of peptidoglycan precursors across the cytoplasmic membrane.

bacteremia  Bacteria circulating in the bloodstream.

Bacteria Domain name for prokaryotes that have unusual chemicals in their cell walls.

bacterial artificial chromosome (BAC) Derivative of the F-plasmid used as vectors to clone DNA fragments as large as 300,000 base pairs in length.

bactericidal  Able to kill bacteria.

bacteriochlorophyll Type of chlorophyll used by purple and green bacteria; absorbs wavelengths of light that penetrate to greater depths and are not used by other photosynthetic organisms.

bacteriophage A virus that infects bacteria; often abbreviated "phage".

bacteriorhodopsin Pigment of some extreme halophiles that absorbs energy from sunlight and uses it to expel protons from the cell, generating a proton gradient.

bacteriostatic  Able to inhibit the growth of bacteria.

balanced pathogenicity Virus-host relationship in which the virus persists in the host without causing obvious harm.

barophiles  Bacteria that can grow under high pressure.

basal body  Structure that anchors the flagella to the cell wall and plasma membrane.

base analog Compound that resembles a purine or pyrimidine base closely enough to be incorporated into DNA in place of a natural base.

base pairing The hydrogen bonding of adenine (A) to thymine (T) and cytosine (C) to guanine (G); occurs between two complementary strands of DNA.

base Refers to the purine or pyrimidine ring structure found in nucleic acids.

basic amino acids Amino acids with more basic (-NH₃⁺) groups than acid (-COO^-) groups.

basophil Leukocyte with large dark-staining granules that contain histamine and other mediators of inflammation; receptors on cell surfaces bind monomers of IgE.

beta (b ) hemolysis Type of hemolysis observed on blood agar that is characterized by a clear zone around a colony.

Beta- (b ) lactam drugs Group of antimicrobial medications that inhibit peptidoglycan synthesis and have a shared chemical structure called a b -lactam ring.

bilayer (or unit) membrane Double layer of phospholipid molecules that forms the major structure of the cytoplasmic (plasma) membrane

binary fission Asexual process of reproduction in which one cell divides into two independent daughter cells.

binding protein Protein that functions in the ABC transport system; resides immediately outside of the cytoplasmic membrane to deliver a given molecule to a specific transport complex within the membrane.

binomial system  System of naming each species of organism with two Latin words.

biochemical oxygen demand (BOD)  Measure of the amount of biologically degradable organic material in water.

biocide Compound such as a disinfectant that is toxic to many forms of life, including microorganisms.

biodiversity Diversity in the number of species of organisms inhabiting an ecosystem.

biofilm Polysaccharide-encased community of microorganisms attached to a surface.

bioinformatics Developing and using computer technology to store, retrieve and analyze nucleotide sequence data.

bioleaching Conversion of metals to a soluble form due to the metabolic oxidation of insoluble metal sulfides by microorganisms such as Thiobacillus species.

biological vector Organism that acts as a host for a disease organism before it is transmitted to another organism; the pathogen can multiply to high numbers within it.

bioluminescence Biological production of light.

biomass  Total weight of all organisms in any particular environment.

bioremediation Process that uses microorganisms to degrade harmful chemicals.

biosphere  The sum of all the regions of the earth where life exists.

biotechnology The use of microbiological and biochemical techniques to solve practical problems and produce more useful products.

biotype A strain that has a characteristic biochemical pattern, which differs from other strains; also called a biovar.

blood agar Type of agar medium that contains red blood cells; a rich medium that can be used to detect hemolysis.

blood-brain barrier Property of the central nervous system blood vessels that restricts passage of infectious agents and certain molecules (such as medications) into the brain and spinal cord.

blunt end The type of DNA ends generated by a restriction enzyme that cuts directly in the middle the recognition sequence.

BOD  Abbreviation for biochemical oxygen demand.

boil Painful localized collection of pus within the skin and subcutaneous tissue; a furuncle.

bone marrow Soft material that fills bone cavities containing stem cells for all blood cells.

botulinum toxin Toxin produced by Clostridium botulinum that can cause a fatal paralysis in people who consume it.

bright field microscope Type of light microscope that illuminates the field of view evenly.

brine Salty water; used to cure fish and meats.

broad-spectrum antimicrobials Antimicrobials that inhibit or kill a wide range of microorganisms, often including both Gram-positive and Gram-negative bacteria.

Bt-toxin Protein crystal naturally produced by the bacterium Bacillus thuringiensis as it forms endospores; toxic to insect larvae that consume it.

bubo Enlarged, tender lymph node characteristic of plague and some venereal diseases.

bubonic plague Form of plague that typically develops when Yersinia pestis is injected via the bite of an infected flea.

budding  Asexual reproductive technique that involves a pushing out of a part of the parent cell that eventually gives rise to a new daughter cell.

buffer  Substance in a solution that acts to prevent changes in pH.

bulking Overgrowth of filamentous microorganisms in sewage at treatment facilities; interferes with the separation of the solid sludge from the liquid effluent.

burst size Number of newly formed virus particles released from a single cell.

C

calcofluor white Fluorescent dye that binds to a component of fungal cells, causing them to fluoresce bright blue.

Calvin cycle Metabolic pathway used by autotrophs to incorporate CO₂ into an organic form; also called the Calvin-Benson cycle.

cAMP  Abbreviation for cyclic AMP.

cancer Abnormally growing cells that can spread from their site of origin, malignant tumors.

candidiasis Fungal diseases caused by Candida albicans.

candle jar Jar in which a lit candle converts some of the O₂ in air to CO₂; used to cultivate capnophiles.

cap A Methylated guanine derivative that is added to the 5’ end of eukaryotic mRNA before transcription is complete

CAP Abbreviation for cyclic AMP-activating protein.

capnophiles Organisms that require increased concentrations of CO₂ (5 to 10%) and approximately 15% oxygen.

capsid Protein coat that surrounds the nucleic acid of a virus.

capsomer The ring-shaped morphological unit of which icosahedral capsids are constructed.

capsule Glycocalyx that is distinct and gelatinous; sometimes correlated with an organism’s ability to cause disease.

carbapenems Group of antimicrobial medications that interferes with peptidoglycan synthesis; very resistant to b -lactamases.

carbohydrate Compounds containing principally carbon, hydrogen and oxygen atoms in a ratio of 1:2:1.

carbon fixation Process of converting inorganic carbon (CO₂) to an organic form. In photosynthetic organisms, the dark or light-independent reactions.

carboxy (or C terminal) The end of the protein molecule that has an unbonded –COOH group.

carbuncle  Painful infection of the skin and subcutaneous tissues, manifests as a cluster of boils.

carrier (1) Type of protein found in cell membranes that transports certain compounds across the membrane; may also be called a permease or transporter protein. (2) A human or other animal that harbors a pathogen without noticeable ill effects.

carrier state State of infection in which the agent can be detected in body fluids without causing disease symptoms.

cascade  In biology, a series of reactions which, once started, continues to the final step by each step triggering the next in a special order; activation of complement is an example.

caseous necrosis Type of localized tissue death having a cheese-like consistency, characteristic of tuberculosis and certain other chronic infectious diseases.

catabolism Cellular processes that harvest the energy released during the breakdown of compounds such as glucose and use that energy to synthesize ATP, the energy currency of all cells.

catabolite repression  Inhibition of gene activity by an efficiently degraded catabolite.

catabolite  Product of catabolism.

catalase Enzyme that breaks down hydrogen peroxide (H₂O₂) to produce water (H₂O) and oxygen gas (O₂).

catalyst  Substance that speeds up the rate of a chemical reaction without being altered or depleted in the process.

cations Positively charged ions.

CD antigens  Abbreviation for cluster of differentiation antigens

CD-4 lymphocytes  T lymphocytes bearing the CD-4 (cluster of differentiation) surface molecules; T helper cells are CD-4.

CD-8 cells  T lymphocytes bearing the CD-8 cluster of differentiation surface molecules; T cytotoxic cells and some T suppressor cells are CD-8 cells.

cDNA DNA obtained by using reverse transcriptase to synthesize DNA from an RNA template in vitro; lacks introns that characterize eukaryotic DNA.

cell culture or tissue culture Cultivation of animal or plant cells in the laboratory .

cell wall Rigid barrier that surrounds a cell, keeping the contents from bursting out. In prokaryotes, peptidoglycan provides rigidity to the cell wall.

cell-mediated immunity (CMI)  Immune responses mediated by T lymphocytes.

cellulose Polymer of glucose subunits; principal structural component of plant cell walls.

central metabolic pathways The amphibolic pathways - glycolysis, the TCA cycle and the pentose phosphate pathway – that are used by most chemoheterotrophs.

cephalosporins Group of antimicrobial medications that interfered with peptidoglycan synthesis.

cestode Tapeworm.

challenge  In immunology, to give an antigen to provoke an immunologic response in
a subject previously sensitized to the antigen.

chancre Sore resulting from an ulcerating infection. The "hard chancre" of primary syphilis is typically firm and painless

chaperones Proteins that help other proteins fold properly.

chemical bond Force that holds atoms together to form molecules.

chemically defined media Bacteriological media composed of ingredients of known chemical composition; generally used for specific experiments when nutrients must be precisely controlled.

chemiosmotic gradient Accumulation of protons on one side of a membrane due to expulsion of protons by the electron transport chain; used to power the synthesis of ATP, fuel certain transport processes and drive the rotation of flagella. Also called the proton motive force.

chemiosmotic theory The theory that a proton gradient is formed by the electron transport chain and is then used to power the synthesis of ATP.

chemoautotrophs  Organisms that use inorganic chemicals as a source of energy and CO₂ as the major source of carbon.

chemoheterotrophs  Organisms that use chemical energy and an organic source of carbon.

chemolithoautotrophs Organisms that obtain energy by degrading reduced inorganic compounds such as hydrogen gas (H₂ ), and use CO₂ as a source of carbon.

chemolithotrophs Organisms that obtain energy by degrading reduced inorganic compounds such as hydrogen gas (H₂ ); in general, chemolithotrophs are chemolithoautotrophs.

chemoorganoheterotrophs Organisms that obtain both energy and carbon from organic compounds.

chemoorganotrophs Organisms that obtain energy by degrading organic compounds such as glucose. In general, chemoorganotrophs are chemoorganoheterotrophs.

chemostat  Device used to grow bacteria in the laboratory that allows nutrients to be added and waste products removed continuously.

chemotaxis Directed movement of an organism in response to a certain chemical in the environment.

chemotherapeutic agent Chemical used as a therapeutic medication to treat a disease.

chemotrophs Organisms that obtain energy by degrading chemical compounds.

chicken pox Disease caused by the herpes virus, varicella.

chloramphenicol Antimicrobial medication that interferes with protein synthesis.

chlorophylls The primary light absorbing pigments used in photosynthesis.

chloroplasts Organelles in photosynthetic eukaryotic cells that harvest the energy of sunlight and use it to release ATP.

chlorosomes Structures of green bacteria in which the light-harvesting pigments are located.

chocolate agar Type of agar medium that contains red blood cells that have been heated under controlled conditions to lyse them, releasing their nutrients; used to culture fastidious bacteria.

cholesterol Sterol found in animal cell membranes; provides rigidity to eukaryotic membranes.

chorea Constant complex, rapid, jerky involuntary movements; an occasional sequel to untreated Streptococcus

chromatin Complex of histones and DNA that make up the chromosomes of eukaryotic cells.

chromosome  Array of genes responsible for the determination and transmission of hereditary characteristics.

chronic infections Infections which develop slowly and persist for months or years.

cilium (pl. cilia) Short, projecting hairlike organelle of locomotion, similar to a flagellum.

circulative transmission Transmission of viruses to plants by insects in which the virus circulates, but does not multiply in the body of the insect.

citric acid cycle Metabolic pathway that incorporates acetyl-CoA, ultimately generating CO₂ and reducing power; also known as the tricarboxylic acid cycle (TCA cycle) and the Krebs cycle.

clade Subtype of a virus such as human immunodeficiency virus (HIV), defined by similar amino acid sequences of their envelope proteins.

class Collection of similar orders; a collection of several classes makes up a phylum.

classical pathway Pathway of complement activation initiated by specific antigen-antibody interaction.

classification Process of arranging organisms into similar or related groups, primarily to provide easy identification and study.

clathrin Proteins that line regions of eukaryotic cell membranes that are internalized during the process of endocytosis.

clonal anergy Inability of a clone of potentially responsive cells to respond immunologically.

clonal deletion Elimination of immature lymphocytes upon binding to self antigens to produce tolerance to self.

clonal selection and expansion Selection and activation of a lymphocyte by interaction of antigen and specific antigen receptor on the lymphocyte surface, causing the lymphocyte to proliferate to form an expanded clone.

clone  Group of cells derived from a single cell.

cloning vehicle  Replicating piece of DNA into which genes of interest are introduced for the purpose of cloning the DNA.

closed system Batch system (such as a tube or flask of broth, or an agar plate) used for growing microorganisms; nutrients are not replenished and wastes are not removed.

clusters of differentiation (CD) antigens Cell-surface antigens identified by clusters or groups of monoclonal antibodies; used to distinguish subgroups of white blood cells

CMI  Abbreviation for cell-mediated immunity

CO₂ fixation Process of converting inorganic carbon (CO₂) to an organic form.

coagulase  Non-enzymatic product of Staphylococcus aureus that clots plasma.

coccus (plural: cocci) Spherical-shaped bacterial cell.

codon Set of three nucleotides.

coenzyme A  Coenzyme involved in decarboxylation.

coenzyme  Small organic molecule that transfers small molecules from one enzyme to another.

cofactor Non-protein component required for the activity of some enzymes.

cohesive ends Single-stranded overhangs generated when DNA is digested with a restriction enzyme that cuts asymmetrically within the recognition sequence; sticky ends.

cohort group Population with a known exposure to a specific risk factor that is followed over time in a prospective study.

coliforms Facultative, nonspore-forming, Gram-negative rods that ferment lactose, producing acid and gas within 48 hours at 35^oC; because most typically reside in the intestine they are used as indicators of fecal pollution.

colonization  Establishment of a site of reproduction of microbes on a material, animal, or person without necessarily resulting in tissue invasion or damage.

colony  Population of bacterial cells arising from a single cell.

colony blot Technique that uses a probe to detect a given DNA sequence in colony.

colony-forming unit A unit that gives rise to a single colony; may be a single cell or multiple cells attached to one another

combination therapy Administration of two antibiotics simultaneously to prevent growth of mutants that might be resisitant to one of the antibiotics

commensalism  Relationship between two organisms in which one partner benefits from the association and the other is unaffected.

commercially sterile Free of all microorganisms capable of growing under normal storage conditions; the endospores of some thermophiles may remain.

common source epidemic Outbreak of disease due to contaminated food, water, or other single source of infectious agent.

communicable diseases Diseases that are spread from an infected animal or person to another animal or person.

communities All of the living organisms in a given area.

competent  Condition in which a bacterial cell is capable of taking up and integrating high molecular weight DNA into its chromosome.

competitive inhibition Type of enzyme inhibition that occurs when the inhibitor competes with the normal substrate for binding to the active site.

complement fixation test  Serological method in which antibody-antigen reactions are detected by the consumption (fixation) of complement.

complement  System of serum proteins that act in sequence, producing biological effects concerned with inflammation, the immune response, and the lysis of cells.

complementary Bases in nucleic acid which hydrogen bond to one another; A (adenine) is complementary to T (thymine) and G (guanine) is complementary to C (cytosine).

complex medium  Medium for growing bacteria that has some ingredients of unknown chemical composition.

compound microscope Microscope that employs two magnifying lenses - an objective lens and an ocular lens. The lenses in combination visually enlarge an object by a factor equal to the product of each lens’ magnification.

condenser lens Lens of a microscope that is used to focus the illumination; positioned between the light source and the specimen and does not effect the magnification.

conditional lethal mutant Mutant which under some environmental conditions will grow but under other conditions will not grow.

confocal scanning laser microscope Type of microscope that focuses a laser beam to illuminate a given point on one vertical plane of a specimen. After successive regions and planes have been scanned, a computer can construct a three-dimensional image of a thick structure.

congenital  A condition existing from the time of birth.

conidia Asexual spores borne on hyphae; produced by fungi and bacteria of the genus Streptomyces.

conjugation Mechanism of gene transfer in bacteria that involves cell-to-cell contact.

conjugative plasmid  Plasmid that carries the genes for sex pili and can transfer copies of itself to other bacteria during conjugation.

consensus sequence Common theme of nucleotides that characterize a stretch of DNA that has a certain function.

constant region  That part of the antibody molecule that does not vary in amino acid sequences among molecules of the same immunoglobulin class.

consumption Stage of biogeochemical recycling in which consumer organisms metabolize the organic materials made by producers.

contact dermatitis A T-cell mediated inflammation of the skin occurring in sensitized individuals as a result of contact with the particular antigen; a form of delayed hypersensitivity.

contagious diseases Diseases that are highly communicable and are spread from one host to another very readily.

continuous culture Method used to maintain cells in a state of uninterrupted growth by continuously adding nutrients and removing waste products; a type of open system.

convalescence Period of recuperation and recovery from an illness.

convergent evolution Process of evolution when two genetically different organisms develop similar environmental adaptations.

co-repressor Molecule that binds to an inactive repressor and, as a consequence, enables it to function as a repressor.

cortex Layer of the endospore that helps maintain the core in a dehydrated state, protecting it from the effects of heat.

counterstain In a differential staining procedure, the stain applied to impart a contrasting color to bacteria that do not retain the primary stain.

covalent bond Strong chemical bond formed by the sharing of electrons between atoms.

critical items Medical instruments such as needles and scalpels that come into direct contact with body tissue.

cross-contamination Transfer of pathogens from one item to another.

cross-sectional study Study that surveys a range of people to determine the prevalence of characteristics including disease, risk factors associated with disease, or previous exposure to a disease-causing agent.

croup Acute obstruction of the larynx occurring mainly in infants and young children, often resulting from respiratory syncytial or other viral infection

crown gall tumor  A tumor on a plant caused by Agrobacterium sp.

CSF  Abbreviation for colony stimulating factor.

curd Coagulated milk proteins, produced during cheese-making.

cyclic AMP-activating protein (CAP)  Protein that binds to cAMP to promote gene transcription.

cyclic photophosphorylation Type of photophosphorylation in which electrons are returned directly to the chlorophyll; used to synthesize ATP without generating reducing power.

cyst Dormant resting protozoan cell characterized by a thickened cell wall.

cysticercus (pl. cysticerci) Cyst-like larval form of tapeworms.

cystitis Inflammation of the urinary bladder.

cytochromes  Proteins that carry electrons usually as members of electron transport chains.

cytokines Low molecular weight regulatory proteins made by cells that affect the behavior of other cells; attach to specific cytokine receptors and are essential for communication between cells.

cytopathic effect  Observable change in a cell in vitro produced by viral action such as lysis of the cell.

cytoplasmic membrane  Flexible structure immediately surrounding the cytoplasm of all cells.

cytoskeleton Dynamic filamentous network that provides structure and shape to eukaryotic cells.

cytotoxic  Kills cells.

D

D value Abbreviation for the decimal reduction time.

dark reactions Process of carbon fixation in photosynthetic organisms; the ATP used to drive the process is obtained in the light reactions; the dark reactions are called the light-independent reactions.

dark repair Enzymes of DNA repair that do not depend on visible light.

dark-field microscope Type of microscope that directs light toward the specimen at an angle, so that only light scattered by the specimen enters the objective lens; material in the specimen stands out as bright objects against a dark background.

death phase  Stage in which the number of viable bacteria in a population decreases at an exponential rate.

decarboxylation Removal of carbon dioxide from a chemical.

decimal reduction time Time required for 90% of the organisms to be killed under specific conditions; D value.

decomposition Stage of biogeochemical recycling in which decomposer organisms digest and convert dead plant and animal material into small molecules that can be used by both consumers and producers.

decontamination Treatment to reduce the number of disease-causing organisms to a level that it is considered safe.

degranulation Release of mediators from granules in the cell, as histamine release from mast cells.

dehydration synthesis Chemical reaction in which H₂O is removed with the result that two molecules are joined together.

dehydrogenation Oxidation reaction in which both an electron and an accompanying proton are removed.

delayed hypersensitivity  Hypersensitivity caused by cytokines released from sensitized T lymphocytes; reactions occur within 48 to 72 hours after exposure of a sensitized individual to antigen.

denaturation (1) Disruption of the three dimensional structure of a protein molecule. (2) The separation of the complementary strands of DNA.

dendritic cells Cells with a branched morphology, some of which are related to macrophages; some are antigen-presenting cells.

denitrification Bacterial conversion of nitrate to gaseous nitrogen by anaerobic respiration.

dental plaque A biofilm on teeth.

deoxyribonucleic acid (DNA) Macromolecule in the cell that carries the genetic information.

depth filter Type of filter with complex, tortuous passages that allow the suspending fluid pass through while retaining microorganisms.

dermatophytes Certain mold-like fungi that live on the skin and can be responsible for disease of the hair, nails, and skin.

descriptive study Type of study that seeks to characterize a disease outbreak by determining the characteristics of the persons involved and the place and time of the outbreak.

diapedesis  Movement of leukocytes from blood vessels into tissues in response to a chemotactic stimulus during inflammation.

diatomaceous earth  Sedimentary soil composed largely of the skeletons of diatoms; contains large amounts of silicon.

diauxic growth Two step growth frequency observed when bacteria are growing in media containing two carbon sources.

dichotomous key Flow chart of tests used for identifying an organism that give either a positive or negative result.

dideoxynucleotide (ddNTP) Nucleotide that lacks the 3' OH group, the portion required for the addition of subsequent nucleotides during DNA synthesis.

differential media Culture media that contain ingredients such as sugars and pH indicators used to distinguish among organisms based on their metabolic traits.

differential staining Type of staining procedure used to distinguish one group of bacteria from another by taking advantage of the fact that certain bacteria have distinctly different chemical structures in some of their components.

diffusion  Movement of molecules from a region of high concentration to a region of low concentration.

diluent Sterile solution used to make the dilutions.

dimorphic Able to assume two forms, as the yeast and mold forms of pathogenic fungi.

diphtheroids Gram-positive cells that are club-shaped and arranged to form V-shapes and palisades; the typical microscopic morphology of Corynebacterium.

diplococci Cocci that typically occur in pairs

direct microscopic count Method of determining the number of bacteria in a measured volume of liquid by counting them microscopically using special glass slides.

direct selection Technique of selecting mutants by plating organisms on a medium on which the desired mutants but not the parent will grow.

directly observed therapy Method used to ensure that patients comply with their antimicrobial therapy; health care workers routinely visit patients in the community and watch them take their drugs.

disaccharide Carbohydrate molecule consisting of two monosaccharide molecules

disease Process resulting in tissue damage or alteration of function, producing body changes noticeable by physical examination or laboratory tests.

disinfectant An agent used to kill pathogenic microbes without necessarily sterilizing the material.

disinfection  Process of reducing or eliminating pathogenic microorganisms or viruses in or on a material so that they are no longer a hazard.

disseminated intravascular coagulation Devastating condition in which clots form in small blood vessels, leading to failure of vital organs.

division Taxonomic rank that groups similar classes; also called a phylum. A collection of similar divisions comprises a kingdom.

DNA Abbreviation for deoxyribonucleic acid.

DNA chip Silicon chip of less than an inch in diameter that can carry an array of hundreds of thousands of oligonucleotides.

DNA fingerprinting The use of characteristic patterns in DNA to match a specimen to a probable source.

DNA gyrase Enzyme that helps relieve the tension in DNA caused by the unwinding of the two strands of the DNA helix.

DNA library Population of cells that together contain the entire cloned chromosome of an organism of interest; each cell can be viewed as containing one "book" of the total genetic information of the organism of interest.

DNA ligase  Enzyme that joins short fragments of DNA.

DNA polymerases Enzymes that synthesize DNA; they use one strand as a template to generate the complementary strand.

DNA probe  A piece of DNA, labeled in some manner, which is used to identify
the presence of similar DNA by hybridizing to it.

DNA replication Duplication of a DNA molecule.

DNA-mediated transformation  Process of gene transfer in which DNA is transferred as a "naked" molecule.

domain Level of taxonomic classification above the kingdom level. There are three domains, Bacteria, Archaea and Eukarya.

donor Refers to the cell that donates DNA in DNA transfer.

double diffusion in gel Qualitative precipitation reaction in which antigen and antibody diffuse toward each other, making a line of precipitation in the area of optimal proportions.

double-blind Type of study where neither the physicians nor the patients know who is receiving the actual treatment.

doubling time Time it takes for the number of cells in population to double; the generation time.

downstream Direction toward the 3’ end of an RNA molecule or the analogous (+) strand of DNA.

droplet transmission Transmission of infectious agents through inhalation of respiratory droplets

Durham tube Small inverted tube placed in a broth of sugar-containing media that is used to detect gas production by a microorganism.

dysentery  Condition characterized by crampy abdominal pain and bloody
diarrhea.

E

E test Modification of the disk diffusion test that utilizes a strip impregnated with a gradient of concentrations of an antimicrobial drug.

eclipse period  Time during which viruses exist within the host cell separated into their protein and nucleic acid components.

ecosystem  An environment and the organisms that inhabit it.

eczema  Condition characterized by a blistery skin rash, with weeping of fluid and formation of crusts, usually due to an allergy.

edema  Swelling of tissues caused by accumulation of fluid.

effector Regulatory molecule that binds to the allosteric site of an enzyme; the binding alters the shape of the enzyme, altering its affinity for the substrate.

electrochemical gradient A separation of charged ions across the membrane.

electron Negatively charged component of an atom which orbits the nucleus.

electron microscope Microscope that uses electrons instead of light and can magnify images in excess of 100,000X.

electron transport chain  Series of electron carriers that transfer electrons from donors such as NADH to acceptors such as oxygen.

electrophoresis  Technique for separating proteins based on the fact that proteins differ in their electrical charges and so will move at different rates in an electrical field.

electroporation Process of treating cells with an electric current to introduce DNA into them.

elementary body Small dense-appearing infectious form of Chlamydia species that is released upon death and rupture of the host cell.

elephantiasis Massive enlargement of the legs and/or external genitalia due to lymphatic obstruction, caused by the inflammatory response to larval roundworms such as Wuchereria bancrofti.

ELISA  Abbreviation for enzyme-linked immunosorbent assay.

Embden-Meyerhof pathway Metabolic pathway that oxidizes glucose to pyruvate, generating ATP and reducing power; also known as glycolysis and the glycolytic pathway.

emerging diseases Diseases that have increased in incidence in the past two decades.

encephalitis Inflammation of the brain.

end product repression  Inhibition of gene activity by the end product of a biosynthetic pathway.

endemic  Constantly present in a population.

endergonic Chemical reaction that requires a net input of energy because the products have more free energy than the reactants.

endocarditis Inflammation of the heart valves or lining of the heart chambers.

endocytosis  Process by which cells take up particles by enclosing them in a vesicle pinched off from the cell membrane.

endoplasmic reticulum  Internal membrane of a eukaryotic cell to which ribosomes are attached.

endosome Vesicle formed when a cell takes up material from the surrounding environment using the process of endocytosis.

endospore  A kind of resting cell, characteristic of a limited number of bacterial species; highly resistant to heat, radiation, and disinfectants.

endosymbiont Microorganism that resides within another cell, providing a benefit to the host cell.

endosymbiont theory Theory that the ancestors of mitochondria and chloroplasts were bacteria that had been residing within other cells in a mutually beneficial partnership.

endotoxin A compound (lipid A) within the outer membrane of Gram-negative that elicits symptoms characteristic of infections caused by live bacteria.

energy The capacity to do work.

energy source Compound that is oxidized by a cell to release energy; also called an electron donor.

enrichment culture Culture method that provides conditions to enhance the growth of one particular organism in a mixed population.

enterics A common name for members of the family Enterobacteriaceae.

Entner-Doudoroff pathway  Pathway that converts glucose to pyruvate and glyceraldehyde-3-phosphate by producing 6-phosphogluconate and then dehydrating it.

enterotoxin  Poisonous substance, usually of bacterial origin, that acts on the intestinal lining cells to cause diarrhea and vomiting.

entropy The degree of disorder in a system.

envelope Structure that surrounds the cytoplasm of the cell; includes the capsule, cell wall and cytoplasmic membrane.

enveloped viruses Viruses that have a double layer of lipid surrounding their nucleocapsid

enzyme A protein catalyst.

enzyme-linked immunosorbent assay (ELISA)  Technique used for detecting and quantifying specific antigens or antibodies by using an antibody labeled with an enzyme.

enzyme-substrate complex Transient form that occurs in an enzyme-mediated reaction, as the enzyme converts a substrate into a product.

EPA  Abbreviation for Environmental Protection Agency, a federal agency.

epidemic A disease or other occurrence whose incidence is higher than expected within a region or population.

epidemiology  The study of factors influencing the frequency and distribution of diseases.

episome  A DNA molecule that can exist either covalently bonded to the bacterial chromosome or in an extrachromosomal state.

epitope Area of an antigen molecule that stimulates the production of, and combines with, specific antibodies.

ergosterol Sterol found in fungal cell membranes; the target of many antifungal drugs.

ergot Poisonous substance produced by the fungus that causes rye smut.

erythrocytes  Red blood cells.

E-site (exit site) Site on the ribosome from which tRNAs exit after donating their amino acid to the adjacent tRNA

ester bond Covalent bond formed between a –COOH group and an –OH group with the removal of H₂O

ethambutol Antimycobacterial drug that inhibits enzymes required for synthesis of mycobacterial cell wall components.

ethidium bromide Mutagenic dye that binds to nucleic acid by intercalating between the bases; ethidium bromide-stained DNA is fluorescent when viewed with UV light.

eubacteria  True bacteria as distinguished from archaebacteria.

Eukarya Name of the domain comprising eukaryotic organisms.

eukaryote  Complex cell type differing from a prokaryote mainly in having a nuclear membrane.

Euryarchaeota Phylogenetic group of the domain Archaea.

eutrophication  Nutrient enrichment leading to the overproduction of algae.

exanthema  A skin rash.

excision repair Mechanism of DNA repair in which a fragment of single-stranded DNA containing mismatched bases is cut out.

exergonic Chemical reaction that releases energy because the starting compounds have more free energy than the products.

exocytosis Process by which eukaryotic cells expel material; membrane-bound vesicles inside the cell fuse with the plasma membrane, releasing their contents to the external medium.

exoenzyme Enzyme that acts outside the cell that produces it.

exoerythrocytic Occurring outside the red blood cells, as the developmental cycle in malaria that occurs in the liver.

exons Portions of eukaryotic genes that are expressed; interrupted by introns.

exotoxin  Soluble poisonous protein substance released by a microorganism.

experimental study Type of study done to assess the effectiveness of measures to prevent or treat disease.

exponential phase Stage of growth of a bacterial culture in which cells are multiplying exponentially; log phase.

expression vectors Vectors that facilitate transcription and translation of cloned DNA.

external node Point on a phylogenetic tree that represents a named species that still exists.

external or temporary transmission Refers to transmission of viruses to plants by insects in which the virus is associated with the external mouth parts of the insect.

extremophiles  Organisms that live under extremes of temperature, barometric pressure, or other environmental conditions.

extrinsic factors Environmental conditions such as the temperature and atmosphere that influence the rate of microbial growth.

F

F^– cell  Recipient bacterial cell in conjugation.

F plasmid Plasmid found in donor cells of E.coli that codes for sex pilus biosynthesis.

F⁺ cell  Donor bacterial cell in conjugation.

Fab (fragment antigen-binding) region Portion of an antibody molecule that binds to the antigen.

facilitated diffusion Transport process that enables movement of impermeable compounds from one side of the membrane to the other by exploiting a concentration gradient; does not require expenditure of energy by the cell.

facultative anaerobe  Organism that grows best in the presence of oxygen (O₂), but can grow in its absence.

facultative Flexible with respect to growth conditions; for example, able to live with or without O₂.

FAD  Abbreviation for flavin adenine dinucleotide.

family  Taxonomic group between order and genus.

fastidious Exacting; refers to organisms that require growth factors.

Fc portion of antibody  Crystallizable end of the constant region of an immunoglobulin molecule; responsible for binding to Fc receptors on cells, for initiating the classical pathway of complement activation and other biological functions.

fecal coliforms Thermotolerant coliform bacteria.

fecal-oral transmission Transmitting organisms that colonize the intestine by ingesting fecally contaminated material.

feedback inhibition  Inhibition of the first enzyme of a biosynthetic pathway by the end product of the pathway; Also called allosteric or end product inhibition.

feeding tolerance Lack of immune response to a specific antigen resulting from introducing the antigen orally.

fermentation  Metabolic process in which the final electron acceptor is an organic compound.

fertility or F plasmid Plasmid found in donor cells of E. coli which codes for the sex pilus and makes the cell F⁺

fever An increase in internal body temperature to 37.8o C or higher.

fibronectin Glycoprotein occurring on the surface of cells and also in a circulating form that adheres tightly to medical devices. Certain pathogens attach to it to initiate colonization.

filterable viruses The old terminology for viruses

fimbria (plural fimbriae) Type of pilus that enables cells to attach to a specific surface.

first-line antimicrobials In antimycobacterial drug therapy, the group of antimicrobials that is preferred because they that are most effective as well as least toxic.

flagellin Protein subunits that make up the filament of flagella.

Flagellum (pl. flagella) (1) In prokaryotic cells, a long protein appendage composed of subunits of flagellin that provides a mechanism of motility; (2) In eukaryotic cells, a long whiplike appendage composed of microtubules in a 9 + 2 arrangement that provides a mechanism of locomotion.

flavin adenine dinucleotide (FAD)  A derivative of the vitamin riboflavin.

flow cytometer Instrument that counts cells in a suspension by measuring the scattering of light by individual cells as they pass by a laser.

fluid mosaic model Model that describes the dynamic nature of the cytoplasmic membrane.

fluke Short, non-segmented, bilaterally symmetrical flatworm

fluorescence microscope Special type of microscope used to observe cells that have been stained or tagged with fluorescent dyes.

fluorescence-activated cell sorter (FACS) Machine that sorts fluorescent-labeled cells in a mixture by passing single cells in a stream past photodetectors.

fluoroquinolones Group of antimicrobial drugs that interferes with nucleic acid synthesis.

fomites  Inanimate objects such as books, tools, or towels that can act as transmitters of pathogenic microorganisms or viruses.

foraminifera Protozoa that have silicon or calcium in their cell walls.

forespore Portion of the endospore formed during the process of sporulation that will ultimately become the core of the endospore.

fowl cholera Worldwide septicemic illness of wild and domestic fowl, caused by Pasteurella multocida; focus of the discovery by Pasteur that an attenuated organism could be used as a vaccine.

fragmentation  Form of asexual reproduction in which a filament composed of a string of cells breaks apart, forming multiple reproductive units.

frame shift mutation Mutation resulting from the addition or deletion of nucleotides.

free energy. Amount of energy that can be gained by breaking the bonds of a chemical; does not include the energy that is always lost as heat.

freeze-etching. Process used to prepare specimens for transmission electron microscopy that allows the shape of underlying regions within structures of a cell to be viewed.

fruiting body With respect to myxobacteria, a complex aggregate of cells, visible to the naked eye, produced when nutrients or water are depleted.

fungemia Fungi circulating in the bloodstream.

Fungicide Kills fungi; used to describe the effects of some antimicrobial chemicals.

fungistatic  Able to inhibit the growth of fungi.

fungus  (pl. fungi) An organism of the Kingdom Fungi, a nonchlorophyllic, eukaryotic heterotroph.

furuncle  A boil; a localized skin infection that penetrates into the subcutaneous tissue, usually caused by S. aureus.

G

G + C content Percentage of guanine plus cytosine in double-stranded DNA; also called the GC content.

GALT Abbreviation for gut-associated lymphoid tissue

gametes Haploid cells that fuse with other gametes to form the diploid zygote in sexual reproduction.

gamma globulin  Portion of blood serum proteins that is separated by electrophoresis and contains most of the immunoglobulins of the blood.

gas chromatography  Technique of separating and identifying gaseous components of a substance.

gas vesicles Small rigid compartments produced by some aquatic bacteria that provide buoyancy to the cell. Gases, but not water, flow freely into the vesicles, thereby decreasing the density of the cell.

gastroenteritis  Acute inflammation of the stomach and intestines; often applied to the syndrome of nausea, vomiting, diarrhea, and abdominal pain.

gel electrophoresis Technique that uses electric current to separate either DNA fragments or proteins according to size by drawing them through a slab of gel, which has the consistency of very firm gelatin.

gene The functional unit of a genome.

gene cloning  Procedure by which genes are inserted into a replicon such as a plasmid or bacteriophage which is then introduced into cells where the replicon can replicate.

gene library  Sum total of all of the genes of an organism that have been inserted into cloning vectors.

general paresis Group of symptoms arising from nervous system damage, usually occurring 10 to 20 years after contracting syphilis; often manifest by emotional instability, memory loss, hallucinations, abnormalities of the eyes, and paralysis.

general secretory pathway Primary mechanism bacterial cells use to secrete proteins; those destined for secretion are recognized by their characteristic sequence of amino acids that make up the amino terminal end.

generalized transducing phage  Bacteriophage that is capable of transferring any part of the bacterial chromosome from one cell to another. (By contrast, a specialized transducing phage transfers only specific parts of the genome.)

generalized transduction Transfer of any bacterial gene to other bacteria by phage.

generation time Time it takes for the number of cells in a population to double; doubling time.

genetic engineering  Process of deliberately altering an organism’s genetic information by changing its nucleic acid sequences.

genetic reassortment Exchange of genetic information following two different segmented viruses infecting the same cell.

genetic recombination The joining together of genes from different organisms.

genetics The study of the function and transfer of genes.

genome Complete set of genetic information in a cell.

genome mining Searching genomic databases. For example, companies might search genomic databases to locate ORFs that may encode proteins of medical value.

genomics Study and analysis of the nucleotide sequence of DNA.

genus (pl. genera) Category of related organisms, usually containing several species. The first name of an organism in the Binomial System of Classification

germicide  Agent that kills microorganisms and inactivates viruses.

germination  Sum total of the biochemical and morphological changes that an endospore or other resting cell undergoes before becoming a vegetative cell.

giant cell  Very large cell with many nuclei, formed by the fusion of many macrophages during a chronic cell-mediated response; found in granulomas.

gingivitis Inflammation of the gums.

global regulation Simultaneous regulation of numerous unrelated genes; global control.

global repressor  Regulatory protein involved in the control of several different biosynthetic or degradative pathways.

glucose-salts Type of chemically defined medium that contains only glucose and certain inorganic salts; supports the growth of E. coli.

glycan chain High molecular weight linear polymer of alternating subunits of N-acetylglucosamine and N-acetylmuramic acid that serves as the backbone of the peptidoglycan molecule.

glycocalyx Gel-like layer that surrounds some cells and generally functions as a mechanism of either protection or attachment.

glycogen  Polysaccharide composed of glucose molecules.

glycolipids Lipids that have various sugars attached.

glycolysis Metabolic pathway that oxidizes glucose to pyruvate, generating ATP and reducing power; also called the Embden-Meyerhoff pathway and the glycolytic pathway.

glycoproteins Proteins with covalently bonded sugar molecules.

goblet cells Mucus-secreting epithelial cells.

Golgi apparatus Series of membrane-bound flattened sacs within eukaryotic cells that serve as the site where macromolecules that are synthesized in the endoplasmic reticulum are modified before they are transported to other destinations.

Gram stain  Staining technique that divides bacteria into one of two groups, Gram-positive or Gram-negative, on the basis of color. Among eubacteria, the staining reaction correlates well with cell wall structure.

Gram-negative Bacteria that lose the crystal violet in the Gram-stain procedure and therefore stain pink; the cell wall of these organisms is composed of a thin layer of peptidoglycan surrounded by an outer membrane.

Gram-positive Bacteria that retain the crystal violet stain in the Gram-stain procedure and therefore stain purple; the cell wall of these organisms is composed of a thick layer of peptidoglycan.

granulation tissue New tissue formed during healing of an injury, consisting of small, red, translucent nodules containing abundant blood vessels.

granulocytes  White blood cells characterized by the presence of prominent granules; basophil granules stain dark with basophilic dyes, eosinophils stain bright red with eosinophilic dyes, and neutrophils do not take up either stain

granuloma  Found in a chronic cell-mediated response, collections of lymphocytes and stages of macrophages; an attempt by the body to wall off and contain persistent organisms and antigens.

griseofulvin Antifungal medication that appears to interfere with the action of tubulin, a necessary factor in nuclear division.

group translocation Type of transport process that chemically alters a molecule during its passage through the cytoplasmic membrane.

growth curve. Growth pattern observed when cells are grown in a closed system; consists of four stages- lag phase, log phase (or exponential phase), stationary phase, and death phase.

growth factors Compounds that a particular bacterium cannot synthesize and therefore must be included in a medium that supports the growth of that organism.

gumma Localized area of chronic inflammation and necrosis in tertiary syphilis, often manifest as a swelling

gut-associated lymphoid tissue (GALT)  Part of the mucosa-associated lymphoid tissue, found in the intestines including Peyer’s patches, the appendix and some lymph nodes.

H

HAART Highly active anti-retroviral therapy; a cocktail of medications that act at different sites during replication of human immunodeficiency virus.

hairy leukoplakia Whitish patch, usually appearing on the tongue of individuals with severe immunodeficiency, thought to be caused by reactivation of latent Epstein-Barr virus (EBV) infection.

half-life. Time it takes for one-half of the original number of molecules of a compound to be eliminated or degraded.

halophile  Organism that prefers or requires a high salt (NaCl) medium.

haploid. Condition in which each type of chromosome is represented only once.

hapten  Substance that can combine with specific antibodies but cannot incite the production of those antibodies unless it is attached to a large carrier molecule.

haustoria Specialized hypha of parasitic fungi that can penetrate plant or animal cell walls.

helicase Enzyme that unwind the DNA helix ahead of the replication fork.

helminth A parasitic worm.

helper T lymphocytes  CD4+ lymphocytes that provide assistance needed for other cells such as B lymphocytes and macrophages to carry out their functions; T helper cells usually act by producing cytokines.

hemagglutination Clumping of red blood cells.

hematopoietic stem cells Bone marrow cells that give rise to all blood cells.

hemolytic disease of the newborn (HDN) Disease of the fetus or newborn caused by transplacental passage of maternal antibodies against the baby's red blood cells, resulting in red cell destruction; usually anti-Rhesus (Rh) antibodies are involved and the disease is called Rh disease; also called erythroblastosis fetalis.

hemolytic uremic syndrome Serious condition characterized by red cell breakdown and kidney failure, a sequel to infection by certain Shiga toxin producing strains Shigella dysenteriae and Escherichia coli.

hepatitis B virus Formerly called serum hepatitis virus because it can be transmitted from the blood of an infected individual.

herd immunity Phenomenon that occurs when a critical concentration of immune hosts prevents the spread of an infectious agent.

hermaphroditic Having both male and female reproductive structures in the same organism.

herpes zoster Another name for shingles; a disease which results from reactivation of the herpes virus causing chickenpox.

heterocyst Specialized non-photosynthetic cells of cyanobacteria within which nitrogen-fixation occurs.

heterofermenters  Bacteria that produce various substances such as ethanol, CO₂, lactic, and other acids from glucose. (Contrast with homofermenters.)

heterophile antibody Antibody that reacts with the red blood cells of another animal

heterotroph Organism that obtains carbon from an organic compound such as glucose.

Hfr cells (high frequency of recombination cells)  Rare cells in the F⁺ population that can transfer their chromosome to an F^– cell.

high copy number plasmid Plasmid whose numbers in the cell range from 50 to 500.

high efficiency particulate air (HEPA) filters Special filters that remove from air nearly all particles, including microorganisms, that have a diameter greater than 0.3 m m.

high-energy phosphate bond Bond that joins a phosphate group to a molecule and releases a relatively high amount of energy when hydrolyzed; denoted by the symbol ~ .

high-level disinfectant Chemical used to destroy all viruses and vegetative cells, but not endospores.

high-temperature-short-time-method (HTST) Most common pasteurization protocol; using this method, milk is pasteurized by holding it at 72^oC for 15 seconds.

histamine  H substance found in basophil and mast cell granules that upon release can cause dilation and increased permeability of blood vessel walls and other effects; a mediator of inflammation.

histocompatibility antigens Cell surface molecules involved in the immunological rejection of transplanted tissues and organs and in recognition between cells during the immune response; also called major histocompatibility (MHC) antigens, and in people, the human leukocyte antigens (HLA).

HIV disease The illness caused by human immunodeficiency virus, marked by gradual impairment of the immune system, ending in AIDS.

HLA  Abbreviation for human leukocyte antigen.

homofermenters  Bacteria that convert glucose into lactic acid as the end product of fermentation.

homologous With respect to DNA, stretches that have similar or identical nucleotide sequences and probably encode similar characteristics.

homologous recombination Genetic recombination between the same genes.

homoserine lactone (HSL) Freely diffusible molecule that is used by bacteria to sense the density of cells within their population.

hook Curved structure that connects the filament of the flagella to the cell surface.

hops Flowers of the vine-like hop plant; they are added to wort to impart a desirable bitter flavor to beer and contribute antibacterial substances.

horizontal evolution With respect to antimicrobial resistance, the acquisition of resistance through gene transfer.

horizontal gene transfer Transmission of DNA from one species to another; also called lateral gene transfer.

horizontal transmission Transfer of a pathogen from one person to another through contact, ingestion of food or water or via a living agent such as an insect is called.

host   Organism on or in which smaller organisms or viruses live, feed, and reproduce; a definitive host is an animal in which the sexually mature form of a parasite occurs; an intermediate host is an animal in which the asexual developmental stages of a parasite occur.

host range Refers to the range of cell types that a pathogen can infect.

HSV-1 (herpes simplex virus-1) Member of the herpes family of viruses that causes cold sores.

HSV-2 (herpes simplex virus-2) Member of the herpes family of viruses that are also called genital herpes.

HTST  Abbreviation for high temperature short time pasteurization.

human leukocyte antigen (HLA)  Group of human cell surface antigens.

humoral immune response Antibody response.

hybridization The annealing of two complementary strands of DNA from different sources to create a hybrid double-stranded molecule.

hybridoma  Cell made by fusing a lymphocyte, such as an antibody-producing B cell, with a cancer cell.

hydrogen bond  Weak attraction between an atom with a strong attraction for electrons and a hydrogen atom that is covalently bonded to another atom which attracts the electron of the hydrogen atom.

hydrogenation Reduction reaction in which an electron and an accompanying proton is added to a molecule.

hydrolysis Chemical reaction in which a molecule is broken down as H₂O is added.

hydrophilic Water loving; soluble in water.

hydrophobic bonds  Weak bonds formed between molecules as a result of their mutual repulsion of water molecules.

hyperimmune globulin Immunoglobulin prepared from the sera of donors with large amounts of antibodies to certain diseases, such as tetanus; used to prevent or treat the disease.

hypersensitivity  Also termed allergy; heightened immune response to antigen.

hyperthermophiles Organisms that have an optimum growth temperature between 70° C and 110°C.

hypervariable regions Small areas in the Fab portion of the immunoglobulin light and heavy polypeptide chains that that bind the antigenic epitope.

hypha (plural hyphae) Threadlike structure that characterizes the growth of most fungi and some bacteria such as members of the genus Streptomyces.

hyposensitization (desensitization) Form of therapy for immediate IgE-mediated allergies in which extremely small but increasing amounts of antigen are injected regularly over a period of months, directing the response from IgE to IgG.

I

icosahedral In virology, refers to a virus with a icosahedral capsid, which has the shape of a regular polyhedron having 20 equilateral triangular faces and 12 corners.

IFN  Abbreviation for interferons

illness Period of time during which symptoms and signs of disease occur.

immune complex  Complex of antigen and antibody bound together, often with some complement components included.

immune serum globulin Immunoglobulin G portion of pooled plasma from many donors, containing a wide variety of antibodies; used to provide passive protection.

immunity Protection against infectious agents and other substances.

immunoassay Tests using immunological reagents such as antigens and antibodies.

immunodeficiency  Inability to produce a normal immune response to antigen.

immunodiffusion tests Precipitation reactions carried out in agarose or other gels.

immunoelectrophoresis  Technique for separating proteins by subjecting the mixture to an electric current followed by diffusion and precipitation in gels using antibodies against the separated proteins.

immunofluorescence  Technique used to identify particular antigens microscopically in cells by the binding of a fluorescent antibody to the antigen.

immunogen Antigen that can induce an immune response.

immunoglobulin Glycoprotein molecules that react specifically with the substance that induced their formation; antibodies.

immunological tolerance State of specific unresponsiveness; failure to respond to a specific antigen, such as self antigen.

immunology The study of immunity, or protection against infectious and other agents, and conditions arising from the mechanisms involved in immunity, such as hypersensitivities.

immunosuppression Nonspecific suppression of acquired immune responses.

in vitro  In a test tube or other container as opposed to inside a living plant or animal.

in vivo  Inside a living plant or animal as opposed to a test tube or other container.

inapparent (subclinical) infections Infections in which symptoms do not occur or are mild enough to go unnoticed.

incidence rate  Number of new cases of a disease within a specific time period in a given population.

inclusion body Microscopically visible structure within a cell representing the site at which an infecting virus replicates; can occur within the nucleus or the cytoplasm

incubation period Interval between entrance of a pathogen into a susceptible host and the onset of illness caused by that pathogen.

index case  First identified case of a disease in an epidemic.

indicator medium  Agar medium containing a component that is changed in a recognizable way by a particular species of microorganism that helps identify the organism.

indirect contact Means of transmitting infectious disease by coughing or sneezing, through food and water, insect bites, and other indirect contact.

indirect selection Technique for isolating mutants and identifying organisms unable to grow on a medium on which the parents do grow; often involves replica plating.

induced With respect to gene expression, a gene product that is synthesized only under certain conditions.

induced mutation Mutation that results from the organism being treated with an agent that alters its DNA.

inducer  Substance that activates transcription of certain genes.

inducible enzyme  Enzyme synthesized only when a substrate on which it can act is present.

induction  Process by which a prophage is excised from the host cell DNA; activation of gene transcription.

infection Growth and multiplication of a parasitic organism or virus in or on the body of the host with or without the production of disease.

infectious disease Disease caused by a microbial or viral infection.

infectious dose  Number of microorganisms or viruses sufficient to establish an infection.

infective dose (ID) Concentration of infective virions. Often expressed as ID₅₀ in which 50 percent of the hosts are infected.

inflammation Nonspecific response to injury characterized by swelling, heat, redness, and pain in the affected area.

initiation complex Complex of a 30S ribosomal subunit, a tRNA that carries f-met, and elongation factors, that comes together at a start codon on mRNA and begins the process of translation.

innate immunity Nonspecific immunity that is not acquired or affected by prior contact with the infectious agent or other material involved and is not mediated by lymphocytes.

innate resistance Resistance of an organism to an antimicrobial medication due to the inherent characteristics of that type organism; also called intrinsic resistance.

inner membrane (1) in prokaryotic cells, the cytoplasmic membrane of Gram-negative bacteria; (2) in eukaryotic cells, the membrane on the interior side of an organelle that has a double-membrane.

insert DNA that is (or will be) joined to a vector to create a recombinant DNA molecule.

inserted repeat  Sequence of nucleotides on one strand of DNA that is identical to DNA on another strand when both are read in the same direction i.e., 5' to 3'; associated with transposable elements.

insertion mutation Mutation resulting from the integration of a transposon into a gene.

insertion sequence (IS) Short piece of DNA that has the ability to move from one site on a DNA molecule to another; simplest type of transposable element.

insulin-dependent diabetes mellitus (IDDM) Diabetes caused by autoimmune destruction of pancreatic cells by cytotoxic T cells.

intercalating agents  Agents that insert themselves between two nucleotides in opposite strands of a DNA double helix.

interference microscope Type of light microscope that employs special optical devices to cause the specimen to appear as a three-dimensional image. An example is the Nomarski differential interference contrast microscope.

interferons Cytokines that induce cells to resist viral replication.

interleukins  Group of proteins produced by macrophages and T cells that regulate growth and differentiation of lymphocytes.

intermediate filaments Component of the eukaryotic cell cytoskeleton

intermediate-level disinfectant Type of chemical used to destroy all vegetative bacteria including mycobacteria, fungi, and most, but not all, viruses.

internal node Branch point on a phylogenetic tree that represents an ancestor to modern organisms.

intranuclear inclusion body  Structure found within the nucleus of cells infected with certain viruses such as the cytomegalovirus.

intrinsic resistance Resistance of an organism to an antimicrobial medication due to inherent characteristics of that type of organism; also called innate resistance.

intron  Part of the eukaryotic chromosome that does not code for a protein; removed from mRNA before the mRNA is translated.

ion Charged atom or molecule

ionic bond Bond formed by the attraction of positively charged atoms or molecules to negatively charged ones

IS  Abbreviation for insertion sequence.

isomer  Molecule with the same number and types of atoms as another but differs in its structure.

isometric Relating to a shape characterized by equal sides

isotope  Form of an element that differs in atomic weight from the form most common in nature

J

Jarisch-Herxheimer reaction Abrupt but transitory worsening of symptoms after starting effective antibacterial treatment, thought to be caused by substances released by the death of the bacteria.

K

kinetic energy Energy of motion.

kingdom Taxonomic rank that groups several phyla or divisions; a collection of similar kingdoms makes up a domain.

Kirby-Bauer disk diffusion test Procedure used to qualitatively determine the susceptibility of a given organism to a battery of different antimicrobial medications.

Koch's Postulates Group of criteria used to determine the cause of an infectious disease by culturing the agent and reproducing the disease.

Koplik’s spots  Lesions of the oral cavity caused by measles virus that resemble a grain of salt on a red base.

Krebs cycle Metabolic pathway that incorporates acetyl-CoA, and generates CO₂ and reducing power; also called the tricarboxylic acid cycle (TCA cycle) and the citric acid cycle.

Kupffer cells  Macrophages of the liver.

L

lac operon Operon that encodes the proteins required for the degradation of lactose; it has served as one of the most important models for studying gene regulation.

lactic acid bacteria Group of Gram-positive bacteria that generate lactic acid as a major end product of their fermentative metabolism.

lactoferrin Iron-binding protein found in leukocytes, saliva, mucus, milk, and other substances; helps defend the body by depriving microorganisms of iron.

lactose  Disaccharide consisting of one molecule of glucose and one of galactose.

lacZ’ gene Gene used to visually determine whether or not a vector contains a fragment inserted into the multiple cloning site.

lag phase  Stage in the growth of a bacterial culture characterized by extensive macromolecule and ATP synthesis but no increase in the number of viable cells.

lagging strand Strand of double-stranded DNA that must be synthesized as a series of discontinuous fragments because of its 5’ to 3’ orientation with respect to the replication fork.

lagooning Sewage treatment method in which sewage is channeled into shallow lagoons, during which time it is stabilized by anaerobic and/or aerobic organisms.

laminar flow hood Biological safety cabinet in which laboratory personnel work with potentially dangerous airborne pathogens; a continuous flow of incoming and outgoing air is filtered through HEPA filters to contain microorganisms within the cabinet.

Lancefield grouping Classification of b-hemolytic streptococci based on serological identification

langerhans cells  Antigen-presenting dendritic cells of the skin, similar in some respects to macrophages.

latent infection  Infection in which the infectious agent is present but not active

lateral gene transfer Transfer of DNA from one prokaryotic species to another; also called horizontal gene transfer.

laws of thermodynamics The fundamental principles of energy relationships. The first of these laws states that the energy in the universe can never be created or destroyed. The second states that entropy always increases.

leading strand. Strand of double-stranded DNA that, because of its 5’ to 3’ orientation with respect to the replication fork, is synthesized continuously.

leaky Refers to a mutation in which the mutant gene codes for a protein that is partially functional.

lecithin Component of mammalian cell walls; attacked by the a-toxin of Clostridium perfringens and other lecithinases.

lectin pathway Pathway of complement activation nonspecifically initiated by a host protein binding to mannose present in many bacterial cell walls.

leghemoglobin Protein synthesized by leguminous plants that carries O₂ within a Rhizobium-harboring nodule.

legume Any of a large family of dicotyledonous plants that bear nodules on the roots that contain nitrogen-fixing bacteria, including important food and forage plants (peas, beans, and clovers).

lethal dose (LD) Concentration of lethal virions. Often expressed as LD₅₀; the concentration of virus in which 50 percent of the hosts are killed

leukemia  Cancer of the leukocytes (white blood cells).

leukocidins  Substances that kill white blood cells.

leukocytes White blood cells.

leukotrienes  Substances active in inflammation, leading to chemotaxis and increased vascular permeability; produced by mast cells, basophils and macrophages.

L-forms  Bacterial variants that have lost the ability to synthesize the peptidoglycan portion of their cell wall.

lichen Organism composed of a fungus in a symbiotic association with either a green alga or a cyanobacterium.

light microscope Microscope that uses visible light to illuminate objects.

light reactions Processes used by phototrophs to harvest energy from sunlight; the energy-gathering component of photosynthesis; also called light-dependent reactions.

light repair Process by which bacteria repair UV damage to their DNA only in the presence of light.

light-dependent reactions Processes used by phototrophs to harvest energy from sunlight; the energy-gathering component of photosynthesis.

light-independent reactions Stage of photosynthesis in which the ATP generated in the light-dependant reactions is used to fix CO₂; also called dark reactions.

lincosamides Group of antimicrobials that interferes with protein synthesis.

lipid A Portion of lipopolysaccharide (LPS) that forms the outer leaflet in the lipid bilayer of the outer membrane of Gram-negative cells. It plays an important role in our body’s ability to recognize the presence of invading bacteria, but is also responsible for the toxic effects of LPS.

lipid One of a diverse group of organic substances all of which are relatively insoluble in water, but soluble in alcohol, ether, chloroform or other fat solvents.

lipopolysaccharide (LPS)  Molecule formed by bonding of lipid to polysaccharide; a part of the outer membrane of Gram-negative bacteria.

lipoprotein Macromolecule formed by the bonding of lipid to protein

lipoteichoic acids Component of the Gram-positive cell wall that is linked to the cytoplasmic membrane.

lithoheterotroph  Organism that uses an inorganic compound for energy and an organic compound as a source of carbon.

localized infections Infections limited to one site in or on the body, as a furuncle.

log phase  Stage of growth of a bacterial culture in which the cells are multiplying exponentially.

low copy number plasmid Plasmid whose numbers in the cell are one or two copies

low-level disinfectants Type of chemical used to destroy fungi, enveloped viruses and vegetative bacteria except mycobacteria.

LPS Abbreviation for lipopolysaccharide.

LTLT  Abbreviation for low temperature long time pasteurization.

luciferase Enzyme that catalyzes the chemical reactions that produce bioluminescence.

lymph  Clear yellow liquid that flows within lymphatic vessels; generally contains lymphocytes and may contain globules of fat.

lymphadenopathy syndrome (LAS) Marked generalized enlargement of lymph nodes that often occurs at the end of the period of clinical well-being in HIV disease.

lymphocyte  Small, round, or oval white blood cell with a large nucleus and a small amount of cytoplasm; involved in specific immunity.

lymphoid tissues and organs Collections of lymphocytes and related cells involved in immune responses.

lymphokines  Proteins secreted by lymphocytes that act as intracellular mediators of the immune response.

lysate  Remains of cells and virions that are released after lysis of cells.

lyse To burst

lysogenic conversion Change in the properties of bacteria as a result of carrying a prophage

lysogens Bacteria that carry a prophage integrated into their chromosome.

lysosome Membrane-bound structure in eukaryotic cells that contains powerful degradative enzymes.

lysozyme  Enzyme that degrades the peptidoglycan layer of bacterial cell wall.

M

M protein  Heat- and acid-resistant protein found in the cell walls of Group A streptococci.

MacConkey Agar Type of selective and differential bacteriological medium used to isolate Gram-negative rods that typically reside in the intestine

macroenvironment Overall environment in which an organism lives.

macrolides Group of antimicrobial medications that interferes with protein synthesis.

macromolecule Very large molecule composed of repeating subunits.

macrophages Large mononuclear phagocytes of the tissues; professional phagocytes of the mononuclear phagocyte system that can engulf and destroy microorganisms and other extraneous materials, function as antigen-presenting cells, and carry out ADCC (antibody-dependent cellular cytotoxicity)..

magnetotaxis  Movement by bacterial cells containing magnetite crystals in response to a magnetic field.

Major histocompatibility complex (MHC) Cluster of genes coding for key cell-surface proteins important in cell-to-cell recognition. (See histocompatibility antigens).

malaise Vague feeling of uneasiness or discomfort.

malignant tumor Abnormal growth of cells no longer under normal control which have the potential to spread to other parts of the body.

MALT  Abbreviation for mucosal-associated lymphoid tissue

mammalian artificial chromosomes Vectors that can be used to clone large fragments of DNA into animal cells.

Mast cells Granule-containing tissue cells similar in appearance and function to the basophils of the blood, with receptors for the Fc portion of IgE; important in the inflammatory response and immediate allergic reactions.

MBC Abbreviation for minimum bactericidal concentration.

mechanical vector Organism such as a fly that physically moves contaminated material from one location to another.

medium  (pl. media) Any material used for growing organisms.

meiosis Process in eukaryotic cells by which the chromosome number is reduced from diploid (2N) to haploid (1N).

melting Denaturating of double-stranded DNA.

membrane attack complex (MAC) Complex of the later components of complement that inserts through the cell membrane, resulting in lysis of the cell.

membrane filtration Method employing a membrane filter that is used to determine the number of bacteria in a liquid sample with a relatively low number of organisms.

membrane proteins Specialized proteins imbedded in the membrane bilayer; some function as receptors and others function as transport proteins.

memory cells Lymphocytes specific for an antigen that persist in the body after an immune response to that antigen; upon subsequent exposure to the same antigen they must differentiate and usually proliferate to become effector cells.

memory response (anamnestic response) Enhanced immunological response to a second or subsequent dose of antigen.

meninges  Membranes covering the brain and spinal cord.

meningitis Inflammation of the meninges.

merozoite Stage in the life cycle of certain protozoa, such as the malaria-causing Plasmodium species.

mesophiles  Bacteria that grow most rapidly at temperatures between 20° and 45° C.

messenger RNA (mRNA)  Single-stranded RNA synthesized during transcription from DNA that binds to ribosomes and directs the synthesis of protein.

metabolism  Sum total of all the chemical reactions in a cell.

metabolite  Any product of metabolism.

metachromatic granules  Polyphosphate granules found in the cytoplasm of some bacteria that appear as different colors when stained with a basic dye.

methanogens Group of Archaea that generate energy by oxidizing hydrogen gas, using CO₂ as a terminal electron acceptor. This process generates methane (CH_4).

MHC  Abbreviation for major histocompatibility complex.

MIC Abbreviation for minimum inhibitory concentration.

microaerophiles Organisms that require small amounts of oxygen (2% to 10%) for growth, but are inhibited by higher concentrations.

microaerophillic bacteria Bacteria that grow only in 2-10% O2.

microenvironment Environment immediately surrounding an individual microorgaism.

microfilaments Cytoskeleton structures of eukaryotic cells that enable the cell cytoplasm to move.

microtubules Cytoskeleton structures of a eukaryotic cell that form mitotic spindles, cilia and flagella; long hollow cylinders composed of tubulin.

microvillus (pl. microvilli) Tiny cylindrical process from luminal surfaces of cells such as those lining the intestine; increases surface area of the cell.

mineralization Conversion from organic to inorganic form; stabilization.

minimum bactericidal concentration (MBC) Lowest concentration of a specific antimicrobial medication that kills 99.9% of a given strain of bacteria.

minimum inhibitory concentration (MIC) Lowest concentration of a specific antimicrobial medication that prevents the growth of an organism in vitro.

minus (-) strand (1) The DNA strand that is used as a template for RNA synthesis. (2) The complement to the plus (or sense) stand of RNA. Also called the antisense strand.

miracidium First larval form of a fluke, hatching from the ovum as a ciliated organism.

mismatch repair Repair mechanism in which a repair enzyme recognizes improperly hydrogen bonded bases and excizes a short stretch of nucleotides containing these bases.

mitochondria Organelle in eukaryotic cells that releases ATP.

mitogen  Substance that induces mitosis; causes proliferation of cells.

mitosis Nuclear division process in eukaryotic cells that ensures the daughter cells receive the same number of chromosomes as the original parent.

MMWR  Abbreviation for Morbidity and Mortality Weekly Report, published by the Centers for Disease Control (CDC).

mold A filamentous fungus.

mole  Amount of a chemical in grams equal to the atomic weights of all the atoms in a molecule of that chemical and contains 10²³ molecules.

Molecular Postulates Group of criteria used to determine the cause of an infectious disease by using genetic and other molecular techniques.

molecular weight  Relative weight of an atom or molecule based on a scale in which the H atom is assigned the weight of 1.0.

molecule Smallest part of a compound that retains all the properties of the compound.

monobactams Group of antimicrobial medications that interferes with peptidoglycan synthesis; very resistant to b -lactamases.

monocistronic RNA transcript that encodes one gene.

monoclonal antibodies  Antibodies with a single specificity produced in vitro by lymphocytes that have been fused with a type of malignant myeloma cell.

monocytes Mononuclear phagocytes of the blood; part of the mononuclear phagocyte system of professional phagocytes.

monomer  Repeating subunit of a polymer.

mononuclear phagocyte system (MPS) System of mononuclear cells (monocytes and macrophages) scattered throughout the body that are highly efficient at phagocytosis; formerly known as the reticuloendothelial system.

monosaccharide A sugar. A simple carbohydrate generally having the formula CnH2n0n, where n can vary in number from three to eight.

morbidity Illness. Most often expressed as the rate of illness in a given population at risk.

morbidity rate  Number of cases of a specific disease per given population at risk.

Mordant Substance that increases the affinity of cellular components for a dye.

morphology  Form or shape of a particular organism or structure.

mortality Death. Most often expressed as a rate of death in a given population at risk.

mortality rate  Fraction of people who die from a given disease.

most probable number (MPN) method Statistical estimate of cell numbers based on the theory of probability. A sample is successively diluted to determine the point at which subsequent dilutions receive no cells.

mRNA  Messenger RNA

mucociliary escalator  Moving layer of mucus and cilia lining the respiratory tract that traps bacteria and other particles and moves them into the throat.

mucosal-associated lymphoid tissue (MALT)  Lymphoid tissue present in the mucosa of the respiratory, gastrointestinal and genitourinary tracts.

multiple cloning site  Small sequence of DNA that contains several unique restriction enzyme recognition sites into which foreign DNA can be cloned.

mushroom Filamentous multicelled fungus with macroscopic fruiting bodies.

mutagen Any agent that increases the frequency at which DNA is altered (mutated).

mutant Organism that has a changed nucleotide sequence or arrangement of nucleotides in its DNA, resulting in properties which make the organism different from the parent strain.

mutation Modification in the base sequence of DNA in a gene resulting in an alteration in the protein coded by the gene.

mutualism  Association in which both partners benefit.

myasthenia gravis Autoimmune disease characterized by muscle weakness, caused by autoantibodies.

mycelium (pl. mycelia) Tangled, matlike mass of fungal hyphae.

mycology The study of fungi.

mycorrhiza Symbiotic relationship between certain fungi and the roots of plants.

mycosis (pl. mycoses) Disease caused by a fungus.

N

N-acetylglucosamine (NAG) One of the two alternating subunits of the glycan chains that make up peptidoglycan.

NAD  Abbreviation for nicotinamide adenine dinucleotide, a derivative of the vitamin niacin that is important in the transfer of hydrogen atoms in metabolic processes.

NADH Abbreviation for the reduced form of nicotinamide adenine dinucleotide, a diffusible electron carrier.

NADPH Abbreviation for the reduced form of nicotinamide adenine dinucleotide, a diffusible electron carrier.

narrow host range plasmid Plasmid that only replicates in one or a few closely related species of bacteria.

narrow-spectrum antimicrobials Antimicrobial medications that inhibit or kill a limited range of bacteria.

National Molecular Subtyping Network for Foodborne Disease Surveillance Surveillance network established by the Centers for Disease Control to facilitate the tracking of foodborne disease outbreaks

natural killer cell See NK cell.

natural selection Selection by the environment of those cells best able to grow in that environment

necrotic Dead; refers to dead cells or tissues in contact with living cells, as necrotic tissue in wounds.

negative (-) sense strand Strand of RNA that does not act as mRNA; strand of DNA that is not transcribed into mRNA.

negative staining Staining technique that employs an acidic dye to stain the background against which colorless cells can be seen.

Negri body Viral inclusion body characteristic of rabies.

nematodes Round worms.

neurotransmitter  Any of a group of substances released from the terminations of nerve cells when they are stimulated, that cross to the adjacent cell and cause it to be excited or inhibited.

neutralization tests Tests in which antibodies neutralize viruses by preventing them from infecting cells or neutralize toxins by binding to them and making them nontoxic.

neutron Uncharged component of an atom found in the nucleus.

neutrophiles Organisms that can live and multiply within the range of pH 5 (acidic) to pH 8 (basic) and have a pH optimum near neutral (pH 7).

neutrophils (PMNs) Actively phagocytic leukocytes with granules containing antimicrobial and degradative substances that destroy engulfed organisms and materials; professional phagocytes. See polymorphonuclear neutrophils.

nitrification  Conversion of NH₃ to nitrate (NO₃^–).

nitrogen fixation  Conversion of nitrogen gas to ammonia.

NK cell  Large granular, non-T, non-B lymphocyte that can recognize and destroy certain cells that it senses as foreign in a nonspecific fashion.

nodule  Swelling on the root of a leguminous plant caused by Rhizobium; the site of nitrogen fixation.

Nomarski differential interference contrast microscope Type of microscope that has a device for separating light into two beams that pass through the specimen and then recombine. Light waves are out of phase when they recombine, resulting in the three-dimensional appearance of material in the specimen.

nomenclature System of assigning names to organisms; a component of taxonomy.

non-communicable diseases Disease that cannot be transmitted from one individual to another.

non-competitive inhibition Type of enzyme inhibition that results from a molecule binding to the enzyme at a site other than the active site.

non-conjugative plasmid  Plasmid that lacks some of the genetic information required for its transfer to other bacteria by conjugation.

non-critical items Medical instruments and surfaces such as stethoscopes and countertops that only come into contact with unbroken skin

noncyclic photophosphorylation Type of phosphorylation in which high-energy electrons are drawn off to generate reducing power. Electrons must still be returned to chlorophyll, but they must come from a source such as water.

non-polar covalent bond Bond formed by sharing electrons between atoms that have equal attraction for the electrons.

nonspecific immunity Immune responses that are nonspecific with respect to the infectious agent or other material involved, and that are not affected by prior exposures. See innate immunity.

normal microbial flora  That group of microorganisms that colonizes the body surfaces but does not usually cause disease. Also called normal flora.

Northern blot Procedure that is similar in principle to a Southern blot, except that it uses a nucleic acid probe to detect sequences of RNA.

nosocomial infection  Infection acquired during hospitalization.

notifiable diseases Group of diseases that are reported to the CDC by individual states; typically these diseases are of relatively high incidence or otherwise a potential danger to public health.

nuclear membrane  Membrane that separates the nucleus from the cytoplasm in eukaryotic cells.

nucleic acid hybridization Technique in which single strands of DNA are mixed together and allowed to reassociate. The degree to which the single strands reassociate indicates how complementary the strands are to one another.

nucleic acids  Ribonucleic acid (RNA) and deoxyribonucleic acid (DNA).

nucleocapsid Viral nucleic acid and its protein coat.

nucleoid Region of a prokaryotic cell containing the DNA.

nucleolus Region within the nucleus where ribosomal RNAs are synthesized.

Nucleosome Unit of the chromatin of eukaryotic cells that consists of a complex of histones around which the linear DNA wraps twice.

nucleotide array technology Use of a solid support to which a two-dimensional arrangement of numerous different single-stranded DNA fragments of known sequences has been attached.

nucleotides  Basic subunits of ribonucleic or deoxyribonucleic acid consisting of a purine or pyrimidine covalently bonded to ribose or deoxyribose, which is covalently bound to a phosphate molecule.

nucleus Membrane-bound organelle in a eukaryotic cell that contains chromosomes and the nucleolus.

nuisance bloom Odiferous scum caused when buoyant cyanobacteria cells float to the surface of a body of stagnant water, and then lyse and decay.

numerical taxonomy Method of classification based on the phenotypes of prokaryotes; determines the relatedness of different organisms based on the percentage of characteristics that two groups have in common.

O

O antigen Antigenic polysaccharide portion of lipopolysaccharide, the molecule that makes up the outer leaflet of the outer membrane of Gram-negative bacteria.

objective lens Lens of a compound microscope that is closest to the specimen.

obligate aerobes  Organisms with an absolute requirement for oxygen.

obligate anaerobes Organisms that cannot multiply if O₂ is present; they are often killed by traces of O₂ because of its toxic derivatives.

obligate fermenters Organisms that can grow in the presence of O₂ but never use it as a terminal electron acceptor; also called aerotolerant anaerobes.

obligate intracellular parasites Organisms that grow only inside living cells

occlusion bodies Masses of viruses inside or outside cells

ocular lens Lens of a compound microscope that is closest to the eye.

Okazaki fragment Nucleic acid fragment synthesized as a result of the discontinuous replication of the lagging strand of DNA.

oligonucleotide Short chain of nucleotides.

oligosaccharide Short chains of monosaccharide subunits joined together by covalent bonds. Shorter than a polysaccharide.

oligotrophic environment  An environment that is deficient in nutrients.

oligotrophs  Organisms that can grow in a nutrient deficient environment.

oncogene Gene whose activity is involved in turning a normal cell into a cancer cell

open reading frames (ORFs) Stretches of DNA, generally longer than 300 bp, that begin with a start codon and end with a stop codon; they suggest that the region encodes a protein.

open system Method used to maintain cells in a state of continuous growth by continuously adding nutrients and removing waste products; also called a continuous culture

operator Region located immediately downstream of a promoter to which a repressor can bind. Binding of the repressor to the operator effectively prevents RNA polymerase from progressing past that region and blocks transcription.

operon  Group of linked genes that are controlled as a single unit.

opine Unusual amino acid derivative; the portion of the Ti plasmid of Agrobacterium tumefaciens that is transferred to plant cells directs the recipient cells to synthesize this compound.

opportunist  Organism that causes disease only in hosts with impaired defense mechanisms; also called opportunistic pathogens.

opsonization  Enhanced phagocytosis, usually caused by coating of the particle to be ingested with either antibody or complement components.

opthalmia neonatorum Eye infection of newborns caused by Neisseria gonorrhoeae, which is acquired from infected mothers during the birth process.

optical (or stereoisomer) isomer Mirror image of a compound.

optimum growth temperature Temperature at which a microorganism multiplies most rapidly.

order  Taxonomic classification between class and family.

organ   A structure composed of different tissues coordinated to perform a specific function.

organelle A structure within a cell that performs a specific function.

organic matter  Material that contains carbon atoms bonded to other carbon atoms.

origin of replication Distinct region of a DNA molecule at which replication is initiated.

origin of transfer Short stretch of nucleotides, a part of which is transferred first when a plasmid is transferred to a recipient cell; necessary for plasmid transfer.

osmosis Movement of water across a membrane from a dilute solution to a more concentrated solution.

osmotic pressure  Pressure exerted by water on the cytoplasmic membrane due to a difference in the concentration of molecules on each side of the membrane.

osmotolerant Organisms that can tolerate relatively high salt concentrations, up to approximately 10% NaCl.

O-specific polysaccharide side chain The portion of LPS that is directed away from the membrane, at the end opposite of Lipid A; because its composition varies, it can be used to identify species or strains.

outbreak Cluster of cases occurring during a brief time interval and affecting a specific population; may herald the onset of an epidemic.

outer membrane (1) In prokaryotic cells, the unique lipid bilayer of Gram-negative cells that surrounds the peptidoglycan layer. (2) In eukaryotic cells, the membrane on the cytoplasmic side of organelles that have double-membranes.

oxazolidinones Group of antimicrobial drugs that interferes with protein synthesis.

oxidase test Rapid biochemical test used to detect cytochrome c.

oxidation  Removal of an electron.

oxidation-reduction reactions Chemical reactions in which one or more electrons is transferred from one molecule to another; the compound that loses electrons becomes oxidized and the chemical that gains electrons becomes reduced.

oxidative phosphorylation Cellular process that generates energy in the form of ATP, using the proton motive force that is established as electrons are passed along the electron transport chain to a terminal electron acceptor.

oxygenic photosynthesis  Photosynthetic reaction that synthesizes carbohydrate from CO₂ and H₂O with the release of oxygen.

P

palindrome Two stretches of DNA on opposite strands that are identical when oriented in the same direction, i.e. 5’ to 3’ or 3’ to 5’.

pandemic A worldwide epidemic.

para-aminobenzoic acid (PABA) Intermediate in the pathway for folic acid synthesis in bacteria; sulfa drugs have a similar structure to PABA.

parasitism Association in which one organism, the parasite, benefits at the expense of the other organism, the host.

parent strain Refers to the original strain of a bacterium; often used in place of wild type strain.

passive diffusion  Process in which molecules flow freely into and out of a cell so that the concentration of any particular molecule is the same on the inside as it is on the outside of the cell.

passive immunity Protective immunity resulting from the transfer of immune serum or immune cells produced by other individuals or animals.

pasteurization  Process of heating food or other substances under controlled conditions of time and temperature to kill pathogens and reduce the total number of microorganisms without damaging the substance.

pathogen Organism or virus that can cause disease.

pathogenesis  Process by which disease develops.

pathogenicity islands Short fragments of DNA in bacteria that code for factors that cause disease and have been transferred from disease-causing organisms.

peliosis hepatis Serious condition characterized by formation of blood-filled cysts in the liver, caused by Bartonella henselae; usually a complication of AIDS or other severe immunodeficiency.

penicillin enrichment Method for increasing the relative proportion of auxotrophic mutants in a population by killing off the growing prototrophic cells with penicillin.

penicillin  Antibiotic that interferes with the synthesis of the peptidoglycan portion of bacterial cell walls.

penicillin-binding proteins (PBPs) Target of b -lactam antimicrobial drugs; their role in bacteria is peptidoglycan synthesis.

pentamer  Polymer composed of five monomeric structural units.

pentose phosphate pathway Metabolic pathway that converts glucose to pyruvate, generating reducing power in the form of NADPH, and two precursor metabolites.

peptide bond Covalent bond formed between the –COOH group of one amino acid and the –NH₂ group of another amino acid; characteristic of proteins.

peptide interbridge Component of the peptidoglycan layer of Gram-positive bacteria; the short chain of amino acids that links the peptide side chains of adjacent N-acetylmuramic acid molecules.

peptide or P site  First site on the ribosome to which the tRNA binds to begin translation.

peptidoglycan layer Rigid backbone of the bacterial cell wall, composed of repeating subunits of N-acetylmuramic acid and N-acetylglucosamine and a number of amino acids.

peptidoglycan Macromolecule found only in bacteria that provides rigidity to the bacterial cell wall. The basic structure of peptidoglycan is an alternating series of two major subunits N-acetylmuramic acid (NAM) and N-acetylglucosamine (NAG). These chains are cross-linked by peptide chains.

peptone Common component of bacteriological media; consists of proteins originating from any of a variety of sources that have been hydrolyzed to amino acids and short peptides by treatment with enzymes, acids or alkali.

perforin  Molecule produced by T cytotoxic cells and NK cells; functions in killing target cells by forming a pore through the target cell membrane.

periplasm, periplasmic gel  Very narrow gel that lies between the cell wall and the cytoplasmic membrane in Gram-negative bacteria.

peritrichous flagella Distribution of flagella over the entire surface of a cell.

peroxidase enzymes Enzymes found in neutrophil granules, saliva, and milk that together with hydrogen peroxide and halide ions make up an effective antimicrobial system.

persistent Refers to infection in which the causative agent remains in the body for long periods of time often without causing symptoms of disease.

petechia (pl. petechiae) Small purplish spot on the skin or mucous membrane caused by hemorrhage.

Petri dish  Two-part dish of glass or plastic often used to contain medium solidified with agar, on which bacteria are grown.

Peyer’s patches  Collections of lymphoid cells in the gastrointestinal tract; part of the gut-associated lymphoid tissue (GALT) and mucosal-associated lymphoid tissue (MALT).

pH Scale of 0 to 14 that expresses the acidity or alkalinity of a solution.

phage  Abbreviation for bacteriophage.

phage induction Process by which phage DNA is excised from bacterial DNA

phagocytosis, phagocytize  Cellular ingestion of particulate materials within membrane-bound vesicles.

phase contrast microscope Type of light microscope that employs special optical devices to amplify the difference in the refractive indexes of cells and the surrounding medium, increasing the contrast of the image.

phase variation  Reversible change in antigenicity of a structure, such as the flagella of Salmonella species.

phenotypic mixing or transcapsidation Exchange of protein coats by two viruses when two virions infect the same cell

phospholipid Lipid that has a phosphate molecule as part of its structure.

phosphotransferase system Type of group translocation in which the transported molecule is phosphorylated as it passes through the cytoplasmic membrane.

photoautotrophs Organisms that use light as the energy source and CO₂ as the major carbon source.

photoheterotrophs Organisms that use light as the energy source and organic compounds as the carbon source.

photooxidation  Chemical reaction occurring as a result of absorption of light energy in the presence of oxygen.

photophosphorylation Processes that utilize light as an energy source to drive the synthesis of ATP.

photoreactivation (or light repair) Breakage of the covalent bonds joining thymine dimers in the light thereby restoring the DNA to its original state.

photosynthesis Reactions used to harvest the energy of light to form ATP, and then use of that energy to power CO₂ fixation.

photosystems Protein complexes within which chlorophyll and other light-gathering pigments are organized; located in special photosynthetic membranes.

phototaxis Directed movement in response to variations in light.

phototrophs Organisms that use light as a source of energy.

phycobiliproteins Light-harvesting pigments of cyanobacteria; they absorb energy from wavelengths of light that are not well absorbed by chlorophyll.

phylogenetic tree Type of diagram that depicts the evolutionary heritage of organisms.

phylogeny Evolutionary relatedness of organisms.

phylum Collection of similar classes. A collection of similar phya comprises a kingdom. A phylum may also be called a division.

phytoplankton Floating and swimming algae and photosynthetic prokaryotic organisms of lakes and oceans.

pilus (plural pili)   Hairlike appendages on many Gram-negative bacteria that function in conjugation and for attachment.

pinocytosis. Process by which eukaryotic cells take in liquid and small particles from the surrounding environment by internalizing and pinching off small pieces of their own membrane, bringing along a small volume of liquid and any material attached to the membrane.

plankton  Primarily microscopic organisms floating freely in most waters.

plaque  (1) Clear area in a monolayer of cells. (2) In dentistry, a collection of bacteria that adhere to a tooth surface.

plasma Fluid portion of nonclotted blood.

plasma cell  End cell of the B cell series, fully differentiated to produce and secrete large amounts of antibody.

plasma membrane  Semipermeable membrane that surrounds the cytoplasm in a cell; cytoplasmic membrane.

plasmid Small extrachromosomal circular DNA molecule that replicates independently of the chromosome; often codes for antibiotic resistance.

plasmolysis Process in which water diffuses out of a cell, causing the cytoplasm to dehydrate and shrink from the cell wall.

plate count Method used to determine the number of viable cells in a specimen by determining the number of colonies that arise when the specimen is added to an agar medium.

platelets (thrombocytes) Small cell fragments in the blood that are essential for blood clotting; arise from large bone marrow cells called megakaryocytes.

pleomorphic Bacteria that characteristically vary in shape.

pleurisy Inflammation of the pleura, membranes that line the lung and chest cavity; often marked by a sharp pain associated with breathing.

plus (+) strand (1) The DNA strand that is complementary to the strand used as a template for RNA synthesis. (2) Of the two RNA molecules that can theoretically be transcribed from double-stranded DNA, the one that can be translated to make a protein; also called the sense strand.

PMN  Abbreviation for polymorphonuclear neutrophils.

pneumonia Inflammation of the lungs accompanied filling of the air sacs with fluids such as pus and blood

pneumonic plague Disease that develops when Yersinia pestis infects the lungs.

point mutation Mutation in which only a single base pair is involved.

polar covalent bond Bond formed by sharing electrons between atoms that have unequal attraction for the electrons.

polarity (1) The degree of affinity that an atom has for electrons. This results in positive or negative charges on atoms in a molecule. (2) The 5' to 3' directionality of a nucleic acid fragment.

poly A tail Series of approximately 200 adenine derivatives that are added to the 3’ end of a mRNA transcript in eukaryotic cells; thought to stabilize the transcript and enhance translation.

polycistronic (polygenic) Refers to mRNA containing transcripts of many genes in a single molecule.

polymer Large molecules formed by the joining together of repeating small molecules (subunits).

polymerase chain reaction (PCR) Method used to create millions of copies of a given region of DNA in only a matter of hours.

polymorphic Having different distinct forms at various stages of the life cycle.

polymorphonuclear neutrophil (PMN)  Phagocytic cells that together with the macrophages are known as "professional phagocytes." The nuclei of these cells are segmented and composed of several lobes.

polymyxin B Type of antimicrobial medication that damages cytoplasmic membranes.

polypeptide Chain of amino acids joined by peptide bonds; also called a protein.

polyribosome Assembly of multiple ribosomes attached to a single mRNA molecule; also called a polysome.

polysaccharide Long chains of monosaccharide subunits.

polyunsaturated fatty acid Fatty acid that contains numerous double bonds.

porins  Proteins in the outer membrane of Gram-negative bacteria that form channels for small molecules to pass.

portal of entry Place of entry of microorganisms into the host.

portal of exit Place where infectious agents leave the host to find a new host.

positive (+) sense strand Strand of RNA which acts as mRNA. The strand of DNA that gives rise to mRNA.

potential energy Stored energy; it can exist in a variety of forms including chemical bonds, a rock on the top of a hill, and water behind a dam..

pour-plate method  Method of inoculating an agar medium with bacteria while the agar is liquid and then pouring it into a Petri dish where the agar hardens. The colonies grow both on the surface and within the medium.

precipitation reaction  Reaction of an antibody with a soluble antigen to form an insoluble substance.

precursor metabolites Metabolic intermediates that are produced in catabolic pathways but can be siphoned off for use in anabolic pathways.

prevalence Total number cases, both old and new, in a given population at risk at a point in time.

primary culture Cells taken and grown directly from the tissues of an animal.

primary immune response Immune response that occurs upon first exposure to an antigen.

primary infection Infection in a previously healthy individual, such as measles in a child who has not had measles before.

primary lymphoid organs Organs in which lymphoid stem cells mature, including the thymus and bone marrow.

primary metabolites Compounds synthesized by a cell during the log phase.

primary producers Organisms that harvest the energy of sunlight, and use it to convert CO₂ into organic compounds. By doing so, they sustain other life forms, including humans.

primary stain First dye applied in a multi-step differential staining procedures; generally stains all cells.

primary structure Refers to the sequence of amino acids in a protein.

primase Enzyme that synthesizes small fragments of RNA to serve as primers for DNA synthesis during DNA replication.

primer  RNA molecule that initiates the synthesis of DNA.

prion Infectious protein that has no nucleic acid.

production Stage of biogeochemical recycling in which producer organisms convert carbon dioxide or other inorganic compounds into organic materials.

productive infection Virus infection in which more virions are produced.

proglottid One of the segments that make up most of the body of a tapeworm.

prokaryote, prokaryotic Cell characterized by lack of a nuclear membrane and the absence membrane bound organelles.

promoter Nucleotide sequence to which RNA polymerase binds to initiate transcription.

propagated epidemic  Outbreak of contagious disease in which the infectious agent is transmitted to others, resulting in steadily increasing numbers of people becoming ill.

prophage Latent form of a temperate phage whose DNA has been inserted into the host's DNA.

prophylaxis Prevention of disease.

prospective study Study that looks ahead to see if the risk factors identified by a retrospective study predict a tendency to develop the disease.

protease Enzyme that degrades protein; encoded by HIV and the target of several anti-HIV medications.

protein Macromolecule containing one or more polypeptide chains.

Protein A   Protein produced by Staphylococcus aureus that inhibits phagocytosis of the organism by binding to the Fc portion of antibodies.

protist Designation for eukaryotic organisms other than plants, animals and fungi; may be unicellular or multicellular.

proton Positively charged component of an atom found in the nucleus.

proton motive force Form of energy generated by the electron transport chain, which expels protons to create a chemiosmotic gradient.

protooncogene Genes in the bodies of animals that code for proteins that activate transcription.

protoplast Gram-positive cell from which the rigid cell wall has been removed.

prototroph Organism that has no organic growth requirements other than a source of carbon and energy.

protozoa Group of single-celled eukaryotic organisms.

provirus Latent form of a virus in which the viral DNA is incorporated into the chromosome of the host.

pseudopods Transient arm-like extensions formed by phagocytes and protozoa; they surround and enclose extracellular material, including bacteria, during the process of phagocytosis.

P-site (peptidyl site) Site on the ribosome where the tRNA that temporarily carries the elongating amino acid chain resides.

psychrophile  Microorganism that grows best between –5° and 15°C.

psychrotroph Organism that can grow well at low temperatures but has an optimum temperature above 15^oC.

pulsed-field gel electrophoresis Type of gel electrophoresis that is used to separate very large fragments of DNA.

PulseNet Surveillance network established by the Centers for Disease Control to facilitate the tracking of foodborne disease outbreaks; catalogues the RFLPs of certain pathogenic organisms. Also called the National Molecular Subtyping Network for Foodborne Disease Surveillance.

pure culture  Culture that contains only a single strain of an organism.

purine Component of RNA and DNA. The two major purines are adenine and guanine.

pus Thick, opaque, often yellowish material that forms at the site of infection, made up of dead neutrphils and tissue debris.

putrefaction Digestion of proteins by enzymes to yield foul-smelling products.

pyoderma Any skin disease characterized by production of pus.

pyogenic Pus-producing.

pyrimidine Component of RNA and DNA. The three major pyrimidines are thymidine, cytosine and uracil.

pyrogens Fever-inducing substances.

pyruvate End product of glycolysis; a precursor metabolite used in the synthesis of amino acids.

Q

quartenary structure Level of structure of a protein molecule resulting from the interaction of one or more protein chains.

quaternary ammonium compounds Cationic (positively-charged) detergents that are non-toxic enough to be used to disinfect food preparation surfaces. Also called quats.

quorum-sensing Communication between bacteria by means of small molecules, permitting the bacteria to sense when there is an adequate quorum or number of organisms present to activate virulence genes.

R

R plasmids Plasmids that encode resistance to one or more antimicrobial medications.

radial immunodiffusion test Quantitative antigen-antibody precipitation -in -gel test in which one reactant is distributed throughout the gel and the other reactant diffuses into the gel producing a ring of precipitation.

radioallergosorbent test (RAST) Radioimmunoassay that measures the IgE antibody reacting with a specific antigen, used in the diagnosis of immediate allergies.

radioimmunoassay (RIA) Competitive inhibition assay using a radioactively labeled reactant to measure antigens or antibodies.

rDNA DNA that encodes ribosomal RNA (rRNA)

reading frames Grouping of a stretch of nucleotides into sequential triplets. A mRNA molecule has three reading frames, but only one is typically used in translation.

receptor Type of membrane protein that binds to specific molecules in the environment, providing a mechanism for the cell to sense and adjust to its surroundings

receptor-mediated endocytosis Type of pinocytosis that allows cells to internalize extracellular ligands that bind to the cell’s receptors.

recombinant DNA molecule DNA molecule created by joining DNA from two different sources in vitro; a vector-insert chimera is a recombinant DNA molecule.

recombinant vaccines Subunit vaccines produced by genetic engineering.

redox reactions Transfer of electrons from one compound to another; one compound becomes reduced and the other becomes oxidized.

reducing agents Compounds that readily donate electrons to another compound, thereby reducing the other compound.

reducing power Reduced electron carriers such as NADH, NADPH, and FADH₂; their bonds contain a form of usable energy.

reduction  Process of adding electrons and hydrogen atoms to a molecule.

refraction. Bending of light rays that occurs when light passes from one medium to another.

regulatory gene  Gene that functions in the control of the rate of synthesis of other gene products.

regulatory protein Protein that binds to DNA, either blocking or enhancing the function of RNA polymerase.

regulon Set of related genes that are transcribed as separate units but are controlled by the same regulatory protein.

replica plating Technique for the simultaneous transfer of organisms in separated colonies from one medium to another medium.

replication fork In DNA synthesis, the site at which double helix is being unwound to expose the single strands that can function as templates.

replicon Piece of DNA that is capable of replicating; contains an origin of replication.

reporter gene Gene that has a detectable phenotype and can be fused to a gene of interest, providing a mechanism by which to monitor the expression of the gene of interest.

repressible pathway  Pathway in which the enzymes are not synthesized when the end product of the pathway is present.

repressor  Protein that binds to the operator site and prevents transcription.

reservoir  Source of a disease-producing organism.

resistance factor (R factor)  Plasmid that carries genetic information for resistance to one or more chemotherapeutic agents.

resistance plasmid (R plasmid) Plasmid that carries genetic information for resistance to one or more antibiotics and heavy metals.

resolve To clearly separate.

respiration  Sum total of metabolic steps in the degradation of foodstuffs when the electron acceptor is an inorganic compound.

respire To use the processes of respiration.

response regulator Regulatory protein of a two-component regulatory system; receives a phosphoryl group from the membrane-spanning sensor.

restriction endonuclease  Enzyme that recognizes and cuts DNA at specific purine and pyrimidine sites.

restriction enzyme Type of enzyme that recognizes and cleaves a specific sequence of DNA.

restriction fragment length polymorphism (RFLP) Pattern of fragment sizes obtained by digesting DNA with one or more restriction enzymes.

reticulate body Fragile, replicating, non-infectious intracellular form of Chlamydia species.

retrospective study Type of study done following a disease outbreak; compares the actions and events surrounding clinical cases with those of controls.

retroviruses  Group of viruses that carry their genetic information as single-stranded RNA. They have the enzyme reverse transcriptase, which forms a copy of DNA that is then integrated into the host cell chromosome.

reverse transcriptase Enzyme that synthesizes double-stranded DNA complementary to an RNA template.

reversion Process by which a second mutation corrects a defect caused by an earlier mutation.

Reye's syndrome Often fatal condition characterized by vomiting, coma, brain and liver damage, mostly occurring in children treated with aspirin for influenza or chickenpox.

RFLP (Restriction fragment length polymorphism) Pattern of fragment sizes obtained by digesting DNA with one or more restriction enzymes.

rheumatoid arthritis Severe crippling autoimmune disease of the joints, caused by cytokines from inflammatory Th1 cells and immune complexes.

rhizosphere Zone around plant roots containing organic materials exuded by the roots.

rhodamine Fluorescent dye that binds to a compound found only in the cells wall of members of the genus Mycobacterium.

rhuMab (recombinant human monoclonal antibody) Hybrid recombinant anti-IgE molecule being tested in the treatment of asthma.

RIA Abbreviation for radioimmunoassay

ribonucleic acid (RNA) Macromolecules in a cell that play a role in converting the information coded by the DNA into amino acid sequences in protein.

ribose A 5-carbon sugar found in RNA.

ribosomal RNA (rRNA) Type of RNA present in ribosomes; the nucleotide sequences of these are increasingly being used to classify and, in some cases, identify microorganisms.

ribosome Structure that facilitates the joining of amino acids during the process of translation; composed of protein and ribosomal RNA.

ribosome-binding site Sequence of nucleotides on mRNA to which a ribosome binds. The first time the codon for methionine (AUG) appears after that site, translation generally starts.

ribotyping Technique used to distinguish among related strains; detects RFLPs in ribosomal RNA genes.

ribozymes RNA molecules that have a catalytic function.

rifamycins Group of antimicrobial medications that block transcription.

risk factors Specific conditions associated with high frequencies of disease.

RNA polymerase  Enzyme that catalyzes the synthesis of RNA using a DNA template.

RNA  Abbreviation for ribonucleic acid.

RNases Enzymes that degrade RNA.

rod Cylindrical-shaped bacterium; also called a bacillus.

rolling circle replication Mechanism of DNA replication in which a single strand of DNA is synthesized.

rough endoplasmic reticulum Organelle where proteins that are not located in the cytoplasm are synthesized

round worm (or nematode) Helminth that is often parasitic and causes disease.

rRNA  Ribosomal RNA

RTF  Abbreviation for resistance transfer factor.

rubisco Enzyme that initiates the Calvin cycle by joining CO₂ to the 5-carbon compound ribulose 1, 5- bisphosphate.

S

S  unit (for Svedberg) Unit of measurement that expresses the sedimentation rate of a compound; reflects the mass and density of the compound.

salinity  Amount of salt in a solution.

SALT  Skin-associated lymphoid tissues.

sanitize  Process of substantially reducing the microbial populations on objects to acceptably safe public health levels.

saprophyte Organism that lives on dead and decaying matter.

saturated Refers to a fatty acid that contains no double bonds.

scanning electron microscope (SEM) Type of electron microscope that scans a beam of electrons scans back and forth over the surface of a specimen; used for observing surface details, but not internal structures of cells.

scanning probe microscopes Microscope that make it possible to view images at an atomic scale; produces a map showing the bumps and valleys of atoms on a surface.

scanning tunneling microscope Type of scanning probe microscope with a sharp metallic probe that causes electrons to tunnel between the probe and a conductive surface.

schizogony Process of multiple fission in which the nucleus divides a number of times before individual daughter cells are produced.

schizont Multinucleate stage in the development of certain protozoa, such as the ones that cause malaria.

scolex Attachment organ of a tapeworm, the head end.

scrapie  Common name for a neurological disease of sheep thought to be caused by a prion.

sebum  Oily secretion of the sebaceous glands of the skin.

secondary (memory) response Enhanced immune response that occurs upon second or subsequent exposure to specific antigen, caused by the rapid activation of long-lived memory cells. See anamnestic response.

secondary infection Infection that occurs along with or immediately following another infection, usually as a result of the first infection

secondary lymphoid organs Peripheral lymphoid organs throughout the body where mature lymphocytes function in immune responses, including the adenoids, tonsils, spleen, appendix, and lymph nodes, among others.

secondary metabolites Metabolic products synthesized during late-log and stationary phase.

secondary structure Refers to the arrangement of amino acids in a protein. The two major arrangements are helices and sheets.

secretion system Mechanism by which bacterial pathogens transfer gene products into host cells to cause endocytosis or other effects.

segmented virus Virus more than one RNA molecule enclosed in the capsid.

selectable marker  Gene that encodes a selectable phenotype such as antibiotic resistance.

selective enrichment Method of increasing the relative proportion of one particular organism in a mixed population by providing conditions in a broth that enhance the growth of the desired organism and including a selective agent that inhibits the growth of other organisms.

selective medium  Culture medium that favors the growth of a specific microorganism.

selective toxicity Causing greater harm to a pathogen than to the host.

selectively permeable membrane Membrane that allows some but not other molecules to pass through freely.

self assembly Spontaneous formation of a complex structure from its component molecules without the aid of enzymes.

self-transmissible plasmid Plasmid that codes for all of the information necessary for its own transfer.

semiconservative replication Type of nucleic acid replication that results in each of the two double-stranded molecules containing one of the original strands (the template strand) and one newly synthesized strand.

semi-critical items Medical instruments such as endoscopes that come into contact with mucous membranes, but do not penetrate body tissue.

semipermeable  Material that allows the passage of some but not other molecules.

sense strand Of the two RNA molecules that can theoretically be transcribed from double-stranded DNA, the one that can be translated to make a protein; also called the plus (+) strand.

sensitization Prior immunization. Allergic reactions to an antigen occur only in sensitized individuals who have been exposed to that particular antigen.

sepsis A bloodstream infection.

septic tank method Method of treating sewage in which wastes are collected in a large tank and degraded by anaerobic organisms, with the resulting fluid stabilized in a drainage field by aerobic organisms.

septicemia Acute illness caused by infectious agents or their products circulating in the blood stream; blood poisoning.

serial dilutions Series of dilutions, usually twofold or tenfold, used to determine the titer or concentration of a substance in solution.

seroconversion Change from negative serum without specific antibodies to serum positive for specific antibodies.

serogroup Microorganisms within a species that are the same antigenically as determined by specific antisera.

serology Use of serum antibodies to detect and measure antigens, or conversely, the use of antigens to detect serum antibodies.

serotonin  A basic amine, stored in mast cell granules, that upon release can cause contraction of some smooth muscles and increased vascular permeability; a mediator of inflammation.

serotype A strain that has a characteristic antigenic structure that differs from other strains; also called a serovar.

serum  Fluid portion of blood that remains after blood clots.

sex pilus Thin protein appendage required for attachment of one bacterium to another prior to DNA transfer by conjugation.

shake tube Tube of agar medium that has been uniformly inoculated with a bacterial culture in order to determine the oxygen requirement of that organism.

Sheath (1) Tube that surrounds and holds a linear chain of cells; characteristic of some aquatic bacteria. (2) Refers to a rod-like protein component found on many phages; often called a "tail".

shingles (herpes zoster)  Condition resulting from the reactivation of the varicella-zoster virus.

shock Condition with multiple causes characterized by low blood pressure and circulation of the blood inadequate to sustain normal function of vital organs. Septic shock results from growth of microorganisms in the body. Toxic shock results from a circulating exotoxin.

sigma (s ) factor Component of RNA polymerase that is recognizes the promoter.

signal sequence Characteristic series of hydrophobic amino acids at the amino terminal end of proteins that are destined for secretion; functions as a tag, directing transport of the protein through the membrane.

signal transduction Process that transmits information from outside of a cell to the inside, allowing that cell to respond to changing environmental conditions.

signature sequences Characteristic sequences in the genes that encode ribosomal RNA that can be used to classify or identify certain organisms.

signs Effects of a disease observed by examining the patient.

similarity coefficient Numerical value that can be used to classify prokaryotes based on their phenotypic characteristics.

simple diffusion Movement of molecules or ions from a region of high concentration to a region of low concentration;does not involve transport proteins.

simple staining Staining technique that employs a basic dye to impart color to cells.

single-cell protein (SCP) Use of microorganisms such as yeast and bacteria as a protein source.

site specific recombination Mechanism by which a piece of DNA becomes part of a larger piece of DNA;involves identical sequences on each piece of DNA.

skin-associated lymphoid tissue (SALT) Secondary lymphoid tissue consisting of collections of lymphoid cells under the skin.

slime layer Type of glycocalyx that is diffuse and irregular.

slime mold Terrestrial organism that is similar to the fungi but not related genetically.

smear In a staining procedure, the film obtained by placing a drop of a liquid containing a microbe on a glass microscope slide and allowing it to air dry.

smooth endoplasmic reticulum Organelle of eukaryotic cells that is the site of lipid synthesis and degradation and calcium ion storage.

solute Dissolved molecules.

SOS repair Complex, inducible repair process used to repair highly damaged DNA.

Southern blot Technique to detect a given nucleotide sequence in DNA fragments that have been separated by gel electrophoresis and transferred to a membrane filter.

specialized transduction Transfer of only specific bacterial genes by phage from one bacterium to another.

species Group of related isolates or strains; the basic unit of taxonomy. In the binomial nomenclature scheme, the second name given to an organism.

specific immunity  Immune response that depends on the recognition and elimination of foreign antigens by specialized lymphocytes.

spheroplast Gram-negative cell from which the cell wall has been removed; retains some portions of the outer membrane.

spikes or attachment proteins Structures on the outside of the virion that bind to host cell receptors.

spirillum (plural spirilla) Curved rod long enough to form spirals.

spirochete Type of long helical cell with a flexible cell wall that is characterized by an axial filament.

splicing Process that removes introns from eukaryotic precursor RNA to generate mRNA.

spoilage Biochemical changes in foods that are perceived as undesirable.

spontaneous generation  Discredited theory that organisms can arise from nonliving matter.

spontaneous mutation Mutation that occurs naturally without the addition of mutagenic agents.

sporadic Occurring in a population widely spaced in time and place.

spore Type of differentiated, specialized cell formed by certain organisms; includes some types of dormant cells that are resistant to adverse conditions and the reproductive structures formed by fungi.

sporogenesis  In bacteria, a complex, highly-ordered sequence of morphological changes during which a bacterial vegetative cell produces a specialized cell greatly resistant to environmental adversity. Eukaryotes can also experience sporogenesis.

sporozoite Elongated infectious form of certain protozoa; for example, in malaria, the form entering the body from a mosquito bite, infectious for liver cells.

spread plate Technique used to cultivate bacteria by uniformly spreading a suspension of cells onto the surface of an agar plate.

sputum Material coughed from the lungs.

stabilization Conversion of organic to inorganic matter.

start codon Codon at which translation is initiated; in prokaryotes, typically the first AUG after a ribosome-binding site.

starter cultures Strains of microorganisms added to a food to initiate the fermentation process.

stationary phase  Stage of growth of a culture in which the number of viable cells remains constant.

stereoisomer (or optical isomer) Mirror image of a compound.

sterol A type of lipid that has a characteristic structure. Cholesterol is a common sterol.

sterile Completely free of all microorganisms and viruses; an absolute term.

steroid Type of lipid with a specific four-membered ring structure.

sticky ends Single-stranded overhangs generated when DNA is digested with a restriction enzyme that cuts asymmetrically within the recognition sequence. Also called cohesive ends.

stock culture Culture stored for use as an inoculum in later procedures.

stop codon Codon that does not code for an amino acid and is not recognized by a tRNA; signals the end of the protein.

strain  Population of organisms that has characteristics differing from others within the species.

streak plate Simplest and most commonly used technique for isolating bacteria. A series of successive streak patterns is used to sequentially dilute an inoculum on the surface of an agar plate.

streptococcal pyrogenic exotoxins (SPEs) Family of genetically related poisonous proteins produced by certain strains of Streptococcus pyogenes, responsible for scarlet fever, toxic shock and "flesh-eating" necrotizing fasciitis.

stromatolite Coral-like mat of filamentous microorganisms.

structural isomers Molecules that contain the same elements but in different arrangements and not mirror images. Structural isomers have different names.

substrate (1) Substance on which an enzyme acts to form products (2) Surface on which an organism will grow.

substrate level phosphorylation  Transfer of the high-energy phosphate from a phosphorylated compound to ADP to form ATP.

subunit vaccines Vaccines made of products or portions of an agent, bacteria or viruses.

sucrose Disaccharide consisting of a molecule of glucose bonded to fructose; common table sugar

sugar phosphate-backbone Series of alternating sugar and phosphates moieties of a DNA molecule.

sulfa drugs Group of antimicrobial drugs that inhibit folic acid synthesis.

sulfanilamide Antimicrobial drug that inhibits folic acid synthesis; one of the sulfa drugs.

sulfate-reducers Group of obligate anaerobes that use sulfate (SO₄^-2) as a terminal electron acceptor, producing hydrogen sulfide as an end product.

superantigens Molecules that stimulate T lymphocytes by binding to MHC class II molecules and to part of the T cell receptor distinct from the antigen-binding site, resulting in activation of many T cells, overproduction of cytokines, severe reactions, and sometimes fatal shock.

superficial mycoses Fungal infections that affect the hair, skin or nails.

superoxide (O₂^–) Toxic derivative of O₂.

superoxide dismutase Enzyme that degrades superoxide to produce hydrogen peroxide.

swarmer cells Motile cells of sheathed bacteria that disperse to new locations.

symbiosis  The living together of two dissimilar organisms or symbionts.

symporters Transport systems in which the passage of one type of molecule or ion facilitates the transport of another.

symptoms Effects of a disease experienced by the patient.

syncytium (pl. syncytia) Multinucleate body formed by the fusion of cells.

synergistic The acting together of agents to produce an effect greater than the sum of the effects of each agent

synthetic medium  Medium in which the chemical composition and quantity of every component is known

systemic infection Infection in which the infectious agent spreads throughout the body

systemic mycoses Fungal infections that affect the tissues deep in the body.

T

T cells Lymphocytes that mature in the thymus; they originate from stem cells in bone marrow, differentiate in the thymus, and move through the blood stream to secondary lymphoid organs where they are responsible for cellular immune responses and function as helper cells in the antibody response.

T cytotoxic cells  CD8+ lymphocytes that recognize antigen on the surface of target cells and kill the target cells.

T helper (Th) cells  CD4+ T lymphocytes that produce cytokines, influencing and helping the specific immune response; two subgroups are Th1 and Th2.

T suppressor (Ts) cells  T lymphocytes that specifically suppress immune responses, often CD8+ T lymphocytes.

tandem repeat Repetitive core sequence located in regions between human genes; probes that bind to tandem repeats are used in DNA fingerprinting.

tape worm (or cestode) Helminth that is often parasitic and causes disease.

Taq polymerase Heat-stable DNA polymerase of the thermophilic bacterium, Thermus aquaticus.

target DNA In the PCR procedure, the region to be amplified.

tautomeric shift Movement of H atoms from one site on a nitrogenous base to another on DNA; alters the hydrogen bonding properties and therefore, may result in mutations.

taxa  Groups into which organisms are classified.

taxonomy The science that studies organisms in order to arrange them into groups; those organisms with similar properties are grouped together and separated from those that are different. Taxonomy encompasses identification, classification, and nomenclature.

T-cell-dependent antigens Proteins and other antigens that require the cooperation of CD4 Th2 and B cells for the production of antibodies.

T-cell-independent antigens Antigens that can stimulate the production of IgM antibody without the aid of Th cells

T-DNA Portion of the Ti plasmid of Agrobacterium tumefaciens that is typically transferred into a plant cell.

teichoic acids Component of the Gram-positive cell wall, composed of chains of a common subunit, either ribitol-phosphate or glycerol-phosphate, to which various sugars and D-alanine are usually attached.

temperate phage  Bacteriophage that can either become integrated into the host cell DNA as a prophage or replicate outside the host chromosome leading to cell lysis.

terminal electron acceptor Chemical that is ultimately reduced as a consequence of chemotrophic metabolism.

tertiary structure Level of structure of a protein described by its three-dimensional nature. Two major shapes exist, globular and fibrous.

tetracyclines Group of antimicrobial medications that interfere with protein synthesis.

Th1 cells CD4 T lymphocytes called inflammatory T cells because they produce cytokines that drive the development of cytotoxic T cells and that activate macrophages.

Th2 cells CD4 T lymphocytes that produce cytokines that stimulate B cells to produce antibodies.

therapeutic index  Ratio of minimum toxic dose to minimum effective dose of a medication.

thermal death time  Shortest period of time needed to kill all the organisms in
a microbial population at a specific temperature and under defined conditions.

thermophile Organism with an optimum growth temperature between 45°C and 70°C.

thrush Infection of the mouth by Candida albicans.

thylakoids Membrane-bound disc-like structures within the stroma of chloroplasts; they contain chlorophyll.

thymine dimer Two adjacent thymine molecules on the same strand of DNA joined together through covalent bonds.

thymus Primary lymphoid organ located in the upper chest in which T lymphocytes mature.

Ti plasmid (for "tumor inducing") Plasmid of Agrobacterium tumefaciens that enables it to cause tumors in plants. A derivative of the plasmid is used a vector by scientists to introduce DNA into plants.

tissue culture Culture of plant or animal cells that grows in an enriched medium outside the plant or animal.

titer Measure of the concentration of a substance in solution; for example, the amount of a specific antibody in serum, usually measured as the highest dilution of serum that will test positive for antibody.

toxemia Circulation of toxins in the blood stream.

toxin  Poisonous chemical substance.

toxoid  Modified form of a toxin that is no longer toxic but is able to stimulate the production of antibodies that will neutralize the toxin.

trace elements Elements that are required in very minute amounts by all cells; they include cobalt, zinc, copper, molybdenum and manganese.

trachoma Potentially serious chronic eye disease caused by certain strains of Chlamydia trachomatis.

transamination Transfer of an amino group from an amino acid to another organic compound; converts the recipient compound to an amino acid.

transcapsidation or phenotypic mixing Exchange of protein coats in viral assembly when two virions infect the same cell.

transcript Fragment of RNA, synthesized using one of the two strands of DNA as a template.

transcription  Process of transferring genetic information coded in DNA into messenger RNA (mRNA).

transduction Mechanism of gene transfer between bacteria in which bacterial DNA is transferred inside a phage.

transfer RNA (tRNA) Type of RNA that delivers the appropriate amino acid to the ribosome during translation.

transformed cells Containing inheritable changes in bacterial or animal cells.

transfusion reaction Reaction characterized by fever, low blood pressure, pain, nausea, and vomiting, resulting from the transfusion of immunologically incompatible blood.

transgenic Plants and animals into which new DNA has been introduced.

transition step Step in metabolism that links glycolysis to the TCA cycle; converts pyruvate to acetyl-CoA.

translation  Process by which genetic information in the messenger RNA directs the order of amino acids in protein.

translocation Advancement of a ribosome a distance of one codon during translation.

transmissible spongiform encephalopathies Group of fatal neurodegenerative diseases of humans and animals in which brain tissue develops spongelike holes

transmission electron microscope (TEM) Type of microscope that directs a beam of electrons at a specimen; used to observe fine details of cell structure.

transport protein Type of protein found in cell membranes that functions in the transport of certain compounds across the membrane; may be called a permease or a carrier.

transposable element (or transposon) Gene that moves from one DNA molecule to another within the same cell or from one site on a DNA molecule to another site on the same molecule.

transposition  Movement of a piece of DNA from one site in a molecule to another site in the same cell.

trematodes Flatworms known as flukes.

tricarboxylic acid cycle (TCA cycle) Metabolic pathway that incorporates acetyl-CoA, ultimately generating CO₂ and reducing power; also called the Krebs cycle and the citric acid cycle.

trichomes Filamentous multicellular associations of cyanobacteria that may or may not be enclosed within a sheath.

trickling filter method Treatment method for small sewage plants in which a rotating arm of the filter sprays sewage onto a bed of rocks coated with a biofilm of organisms that aerobically degrades the wastes.

triglyceride Molecule consisting of three molecules of the same or different fatty acids bonded to glycerol.

trimethoprim Antimicrobial medication that interferes with folic acid synthesis.

tRNA  Transfer RNA

trophozoite Vegetative feeding form of some protozoa.

trp operon Operon that encodes the five enzymes of the pathway for tryptophan biosynthesis.

tubercle  Granuloma formed in tuberculosis.

tumble Rolling motion of a motile cell that is caused by an abrupt change in the direction of rotation of flagella.

tumor necrosis factors (TNFs) Cytokines with many functions in immune responses; some kill tumor cells.

tumor-inducing (Ti) plasmid Plasmid of Agrobacterium tumefaciens that enables the organism to cause tumors in plants. A derivative of the plasmid is used a vector by scientists to introduce DNA into plants. Also called the Ti plasmid.

turbidity Cloudiness; the turbidity of a bacterial suspension is proportional to the number of cells in that suspension.

tyndallization  Repeated cycles of heating and incubation to kill spore-forming bacteria.

U

ubiquity Widespread prevalence.

UHT  Abbreviation for ultra high temperature pasteurization.

ultra-high-temperature-method (UHT) Protocol designed to render a product free of all microorganisms that can grow under normal storage conditions; technically, not a type of pasteurization.

ultraviolet light (UV)  Electromagnetic radiation with wavelengths between 175 and 350 nm; invisible.

uniporters Transport systems that translocate a single molecule or ion.

unsaturated Refers to a fatty acid with one or more double bonds.

upstream Direction toward the 5’ end of either an RNA molecule or the analogous (+) strand of DNA.

urticaria  Hives; an allergic skin reaction characterized by the formation of itchy red swellings.

UV  Abbreviation for ultraviolet light.

V

vaccine  Preparation of living or dead microorganisms or viruses or their components used to immunize a person or animal against a particular disease.

vancomycin Antimicrobial medication that interferes with peptidoglycan synthesis.

vector (1) In molecular biology, a piece of DNA that acts as a carrier of a cloned fragment of DNA. (2) In epidemiology, any living organism that can carry a disease-causing microbe; most commonly arthropods such as mosquitoes and ticks.

vegetative cell Typical, actively multiplying cell.

vehicle  Inanimate carrier of an infectious agent from one host to another.

vertical evolution Acquisition of antimicrobial resistance through spontaneous mutation.

vertical transmission Transfer of a pathogen from a pregnant woman to the fetus, or from a mother to her infant during childbirth.

vibrio (plural vibrios) Short, curved rod-shaped bacterial cell.

villus (pl. villi) Narrow protrusion from a membrane such as the intestinal lining.

viremia Viruses circulating in the bloodstream.

virion Viral particle in its inert extracellular form.

viroid Piece of RNA that does not have a protein coat but does replicate within living cells.

virulence  Relative ability of a pathogen to overcome body defenses and cause disease; properties of microorganisms that assist pathogenicity.

virus Acellular or non-living agent composed of nucleic acid surrounded by a protein coat.

vitamin  One of a group of organic compounds found in small quantities in natural foodstuffs that are necessary for the growth and reproduction of an organism; usually converted into coenzymes.

volutin Storage form of phosphate found inside certain bacterial cells. Because granules of volutin exhibit characteristic staining with the dye methylene blue, they are called metachromatic granules.

W

water activity (a_w)  Quantitative measure of the water available.

Water molds Non-photosynthetic members of the heterokons; similar to the fungi but not related genetically.

Western blot Procedure that uses a labeled antibody to detect specific proteins; similar in principle to a Southern blot.

whey Liquid portion that remains after milk proteins coagulate during cheese-making.

wide host range plasmid Plasmid that can replicate in unrelated bacteria.

wild type Form of an organism that is isolated from nature.

Y

yeast Unicellular fungus.

yeast artificial chromosome (YAC) Vector that can be used to clone segments of DNA up to a million nucleotides in length and used to introduce foreign DNA into the yeast Saccharomyces cerevisiae.

Z

Z value Increase in temperature required to reduce the decimal reduction time to one-tenth of its initial value.

zone of inhibition Region around a chemical saturated disc where bacteria are unable to grow due to adverse effects of the compound in the disc.

zoonosis (pl. zoonoses) Disease of animals that can be transmitted to humans.

zooplankton Floating and swimming small animals and protozoa found in marine environments, usually in association with the phytoplankton.

zygote Diploid cell formed by the sexual fusion of two haploid cells.