Prescott's Microbiology,4/e

		Microbiology, 4/e Prescott, Harley, Klein
		Instructor Resources

37 Human Diseases Caused Primarily by Gram-Positive and Gram-Negative Bacteria

CHAPTER OVERVIEW

This chapter discusses some of the more important gram-positive and gram-negative bacteria that are pathogenic to humans.

CHAPTER OBJECTIVES

After reading this chapter you should be able to:

! describe bacterial diseases that are transmitted through the air and that involve the respiratory system

! describe bacterial diseases that are transmitted through the air and that cause diseases of the skin or systemic disease

! discuss arthropod-borne bacterial diseases

! discuss bacterial diseases that require direct contact and that usually involve the skin and underlying tissues

! discuss food-borne and waterborne bacterial infections and bacterial intoxications

! discuss diseases and their sequelae such as sepsis and septic shock that cannot be categorized under a specific mode of transmission

CHAPTER OUTLINE

I. Airborne Diseases

A. DiphtheriaCCorynebacterium diphtheriae

1. Usually affects poor people living in crowded conditions

2. Caused by an exotoxin (diphtheria toxin) produced by lysogenized bacteria

3. Symptoms include nasal discharge, fever, cough, and the formation of a pseudomembrane in the throat

4. TreatmentCneutralization of toxin with antitoxin, and penicillin or erythromycin to eliminate the bacteria

5. VaccineCdiphtheria-pertussis-tetanus vaccine (DPT)

6. Eradication may be possible with a vigorous worldwide vaccination campaign, because only humans serve as a reservoir for this organism

B. Legionnaires= disease and Pontiac feverCLegionella pneumophila

1. Legionnaires= disease (legionellosis)

a. Bacteria normally found in soil and aquatic ecosystems

b. Bacteria also found in air-conditioning systems and shower stalls

c. Infection causes cytotoxic damage to lung alveoli

d. Symptoms include fever, cough, headache, neuralgia, and bronchopneumonia

e. Common-source spread

f. Treatment is supportive; administration of erythromycin or rifampin

2. Pontiac fever

a. Resembles an allergic disease more than an infection

b. Symptoms are the same as for legionellosis, but pneumonia does not occur

c. It usually spontaneously resolves in two to five days

C. MeningitisCcaused by a variety of organisms and conditions

1. Bacterial (septic) meningitis is diagnosed by the presence of bacteria in the cerebrospinal fluid

2. Bacterial meningitis is treated with various antibiotics, depending on the specific bacterium involved

3. Aseptic (nonbacterial) meningitis syndrome is more difficult to treat but the mortality is generally low

D. Mycobacterium aviumCM. intracellulaire pneumonia

1. Organisms are normal soil and water inhabitants

2. Both the respiratory and the gastrointestinal tracts have been proposed as portals of entry; the gastrointestinal tract is thought to be the most common site of colonization and dissemination

3. Pulmonary infection is similar to tuberculosis; most often seen in elderly patients with preexisting pulmonary disease

4. Occurs in 15 to 40% of AIDS patients; is becoming a severe problem

5. Symptoms include fever, malaise, weight loss, and diarrhea

6. Treatment is usually multiple drug therapy

E. Pertussis (whooping cough)CBordetella pertussis

1. Highly contagious disease that primarily affects children

2. Transmission is by droplet inhalation

3. Toxins are responsible for most of the symptoms

4. The disease progresses in stages

a. Catarrhal stageCinflamed mucous membranes; resembles a cold

b. Paroxysmal stageCprolonged coughing sieges with inspiratory whoop

c. Convalescent stageCmay take months (some fatalities)

5. Permanent or long-lasting immunity

6. Treatment with erythromycin, tetracycline, or chloramphenicol

7. VaccineCDPT

F. Streptococcal diseasesCAstrep throat,@ scarlet fever, pneumonia, etc.; treated with penicillin, cephalosporin, sulfonamide combination, or erythromycin; no available vaccines except one for streptococcal pneumonia; most streptococcal diseases are caused by varieties of Streptococcus pyogenes

1. Cellulitis, impetigo, and erysipelas

a. CellulitisCdiffuse, spreading infection of subcutaneous tissue characterized by redness and swelling

b. ImpetigoCsuperficial cutaneous infection commonly seen in children

c. ErysipelasCacute infection of the dermis characterized by reddish patches

2. Invasive Streptococcus A infections

a. Dependent on specific strains and predisposing factors

b. Causes necrotizing fascitis that destroys the sheath covering skeletal muscle

c. Also causes myositis, the inflammation and destruction of skeletal muscle and fat tissue

d. Pyogenic exotoxins A and B are produced by 85% of the bacterial isolates

e. Tissues die from lack of oxygen

f. Can also trigger a toxic shocklike syndrome (TSLS) with a mortality rate over 30%

g. Rapid treatment with penicillin G reduces the risk of death

3. Poststreptococcal diseasesConset is one to four weeks after an acute streptococcal infection

a. Glomerulonephritis (Bright=s disease)Cantibody-mediated inflammatory reaction (type III hypersensitivity); may spontaneously heal or may become chronic; possibly a kidney transplant or lifelong renal dialysis may eventually be necessary

b. Rheumatic feverCautoimmune disease involving the heart valves, other parts of the heart joints, subcutaneous tissues and central nervous system; mechanism is unknown; occurs primarily in children ages 6 to 15 years old; therapy is directed at decreasing inflammation and fever, as well as controlling cardiac symptoms and damage

4. Scarlet fever (scarlatina)Cskin-shedding rash mediated by an erythrogenic toxin; caused by a lysogenic bacteriophage; treatment is with penicillin

5. Streptococcal sore throat (strep throat)Cinflammatory response with lysis of erythrocytes and leucocytes; treatment is with penicillin, primarily to minimize the possibility of subsequent rheumatic fever and glomerulonephritis

6. Streptococcal pneumonia

a. Opportunistic (endogenous) infection (caused by S. pneumoniae) from normal microbiota

b. Individuals usually have one of the following predisposing factors:

(1) Viral infection of the respiratory tract

(2) Physical injury to the respiratory tract

(3) Alcoholism

(4) Diabetes

c. Treatment is with penicillin, or erythromycin

d. Vaccine (Pneumovax) is available

G. TuberculosisCMycobacterium tuberculosis

1. Forms nodules (tubercles) in the lungs

2. Diagnosis by isolation of organism, chest X ray, skin test, or DNA probes

3. Chemotherapeutic and prophylactic treatment is isoniazid and rifampin, and streptomycin and/or ethambutol

4. New cases are appearing either by recent transmission (25 to 33%) or by reactivation of old dormant infections (67 to 75%)

5. Multidrug resistant strains are appearing in the population due to spontaneous mutations

II. Arthropod-Borne Diseases

A. Lyme disease (LD, Lyme borreliosis)CBorrelia burgdorferi, B. garinii and B. afzelii

1. Tick-borne, with deer, mice, or the woodrat as the natural reservoir

2. Symptoms include localized rash, flulike symptoms

3. Disease can progress to include heart inflammation, arthritis, and neurological symptoms

4. Years later, it can cause symptoms resembling Alzheimer=s disease and multiple sclerosis with behavioral changes as well

5. Laboratory diagnosis is by isolation of the spirochete, PCR to detect DNA in the urine, or serological testing (ELISA or Western Blot)

6. Treatment with penicillin or tetracycline is effective if administered early

B. PlagueCYersinia pestis

1. Flea-borne, from rodents

2. Sporadic in the U.S. (about 25 cases per year)

3. Bacteria survive and proliferate inside phagocytic cells

4. Symptoms include subcutaneous hemorrhages, fever, and enlarged lymph nodes (buboes)

5. Mortality rate is 50 to 70% if untreated

6. TreatmentCstreptomycin or tetracycline

7. If untreated it may invade lungs (pneumonic plague), resulting in 100% mortality if unrecognized within 12 to 24 hours

8. A vaccine is available for people at high risk

III. Direct Contact Diseases

A. AnthraxCBacillus anthracis

1. Causes ulcerated skin lesions or influenza-like symptoms; headache, fever, and nausea are major symptoms

2. TreatmentCpenicillin, usually in combination with streptomycin; other treatment possibilities are erythromycin or tetracycline; cephalosporius or chloramphenicol

3. VaccineCavailable for animals and persons with high occupational risk

B. Bacterial Vaginosis

1. Disease is sexually transmitted with polymicrobic etiology

2. Autoinfection in women from the rectum, which is inhabited by these organisms

3. Disease is mild but is a risk factor for obstetric infections, various adverse outcomes of pregnancy, and pelvic inflammatory disease

4. Diagnosis is based on fishy odor and microscopic observation of clue cells (sloughed-off vaginal epithelial cells covered with bacteria) in the discharge

5. Treatment is with metronidazole to kill the anaerobes necessary for continuation of the disease

C. Cat Scratch Disease (CSD)

1. Probably caused by Bartonella henselae

2. Diagnosis is based on the clinical history of a cat scratch or bite and subsequent swelling of the regional lymph nodes and by PRR amplification of appropriate gene sequences

3. It is typically self-limiting with abatement of symptoms over a period of days to weeks

D. Chancroid-genital ulcer disease

1. It is sexually transmitted, caused by the gram-negative bacillus, Haemophilus ducreyi

2. The bacterium enters the skin through a break in the epithelium

3. After 4 to 7 days a papular lesion develops with swelling and white blood cell infiltration

4. A pustule forms and ruptures leading to a painful ulcer on the penis or vagina

5. It is a cofactor in the transmission of AIDS

6. Diagnosis is by isolating the bacterium

7. Treatment is with erythromycin or ceftriaxone

8. Prevention is by use of condoms or abstinence

E. Gas gangrene or clostridial myonecrosisCClostridium perfringens

1. Found in soil and intestinal tract microbiota

2. Obligate anaerobe; problem in deep puncture wound where organism can grow readily and produce toxin

3. Tissue necrosis (gangrene) occurs because of the toxin; growth of the organism leads to production of carbon dioxide and hydrogen gas

4. TreatmentCantitoxins, extensive surgical wound debridement, antibiotics, and hyperbaric oxygen

5. Amputation may be necessary to prevent spread

F. GonorrheaCNeisseria gonorrhoeae

1. Sexually transmitted disease of the genitourinary tract, eye, rectum, and throat

2. Invades mucosal cells, causes inflammation and formation of pus

3. MalesCurethral discharge; painful, burning urination

4. FemalesCfrequently asymptomatic; some vaginal discharge; may lead to pelvic inflammatory disease (PID)

5. Infection, if disseminated through the bloodstream can involve other organs

6. Birth through infected vagina can result in neonatal eye infections (ophthalmia neonatorum, or conjunctivitis of the newborn) leading to possible blindness

7. Diagnosis is by culture of the organism and/or use of a DNA probe

8. TreatmentCseveral combination antibiotic treatment regimens have been found to be effective; silver nitrate is often used in the eyes of newborns to prevent infection

9. Control by public education, diagnosis, treatment of symptomatic and asymptomatic individuals, and use of condoms

G. LeprosyCMycobacterium leprae

1. Severely disfiguring skin disease

2. Usually requires prolonged exposure to nasal secretion of heavy bacteria shedders

3. The incubation period may be three to five years, or even longer

4. Starts as skin lesion and progresses slowly; most lesions heal spontaneously, those that don=t are of two types:

a. Tuberculoid (neural)Cmild, nonprogressive, delayed-type hypersensitivity

b. Lepromatous (progressive)Crelentlessly progressive disfigurement

5. Diagnosis is by observation in biopsy specimens and by serodiagnostic tests

6. TreatmentClong-term use of sulfa drugs (diacetyl/dapsone), rifampin, and clofazimine

7. Control by identification and treatment of patients

8. Children of contagious parents should be given prophylactic drug therapy until their parents are treated and have become noninfectious

H. Peptic ulcer disease and gastritisCHelicobacter pylori

1. The evidence of pathogenicity of this organism is now very strong, if not overwhelming

2. Alters gastric pH to favor its own growth near the mucosal cells

3. Colonizes gastric mucus-secreting cells

4. Releases toxins that damage epithelial mucosal cells

5. Transmission is probably propagated, but common source has not been definitively ruled out

6. Diagnosis is by culture of gastric biopsy specimens and serological testing

7. Treatment includes antibiotics and bismuth subsalicylate (Pepto-Bismol)

I. Staphylococcal diseases

1. Staphylococci are facultative anaerobes and are usually catalase positive

2. S. aureusCcoagulase positive, pathogenic; causes severe chronic infections

3. S. epidermidisCcoagulase negative, less invasive, opportunistic pathogens associated with nosocomial infections

4. Many of the pathogenic strains are slime producers (SP); slime is a viscous extracellular glycoconjugate that allows the bacteria to adhere to smooth surfaces such as medical prostheses and catheters

5. Slime producers form biofilms on prosthetic devices

6. Slime also inhibits neutrophil chemotaxis, phagocytosis and the antimicrobial agents vancomycin and teicoplanin

7. Disease can be produced in any organ of the body but is most likely to occur in individuals whose defenses have been compromised

8. They produce exotoxins and substances that promote invasiveness

9. Can cause food poisoning, localized abscesses, impetigo contagiosum, toxic shock syndrome, and staphylococcal scalded skin syndrome

10. Diagnosis is by culture identification, catalase and coagulase tests, serology, DNA fingerprinting, and phage typing

11. Several antibiotics can be used for treatment but isolates should be tested for sensitivity because of the existence of many drug-resistant strains

J. SyphilisCTreponema pallidum

1. Sexually transmitted or congenitally acquired in utero

2. Disease progresses in stages

a. Primary stageClesion (chancre) at infection site that can transmit organism during sexual intercourse

b. Secondary stageCskin rash and other, more general symptoms

c. Latent stageCnot communicable after two to four years except possibly congenitally

d. Tertiary stageCdegenerative lesions (gummas) in the skin, bone, and nervous system

3. Diagnosed by clinical history, microscopic examination, and serology

4. TreatmentCpenicillin in early stages, tertiary stage is highly resistant to treatment

5. Immunity is incomplete

6. Control is by public education, treatment, follow-up on sources and contacts, sexual hygiene, and prophylaxis (use of condoms)

K. TetanusCClostridium tetani

1. Found in soil, dust, hospital environments, and mammalian feces

2. Low invasiveness, but in deep tissues with low oxygen tension, the spores germinate; when the vegetative cells lyse, they release tetanospasmin (an exotoxin)

3. Toxin causes prolonged muscle spasms

4. A hemolysin (tetanolysin) is also produced

5. Prevention is important and involves:

a. Active immunization with toxoid (DPT)

b. Debridement of wounds

c. Prophylactic use of antitoxin

d. Administration of penicillin

L. TularemiaCFrancisella tularensis is spread from animal reservoirs by a variety of mechanisms; a vaccine is available for high-risk laboratory workers

IV. Food-Borne and Waterborne Diseases

A. CholeraCVibrio cholerae

1. Bacteria adhere to the intestinal mucosa of the small intestine

2. They are not invasive, but secrete cholera enterotoxin (choleragen)

3. Choleragen stimulates hypersecretion of water and chloride ions, while inhibiting adsorption of sodium ions; leads to fluid loss

4. Death may result from volume depletion-induced increased protein concentrations in blood, causing circulatory shock and collapse

5. Diagnosis is by culture of the bacterium from feces and serotyping

6. Treatment is rehydration therapy (fluid and electrolyte replacement) plus tetracycline or chloramphenicol

7. With treatment, mortality rate is reduced from higher than 50% (untreated) to less than 1% (treated)

8. Control is based on proper sanitation

B. BotulismCClostridium botulinum

1. Food toxication (poisoning)

2. Frequently caused by canned foods that contain endospores, which germinate and produce an exotoxin (neurotoxin)

3. Can cause death by respiratory or cardiac failure

4. Diagnosis is by hemagglutination testing or toxigenicity testing in animals using the patient=s serum, stools, or vomitus

5. Treatment is supportive; also antitoxin administration

6. Control involves safe food processing practices in the food industry and in home canning; also not feeding honey to babies under one year of age helps prevents infant botulism

C. Campylobacter jejuni gastroenteritis (campylobacteriosis)

1. Transmitted by contaminated food or water, contact with infected animals, or anal-oral sexual activity

2. Causes diarrhea, fever, intestinal inflammation and ulceration, and bloody stools

3. Treatment is supportive, with fluid and electrolyte replacement

4. Erythromycin is used in severe cases, but disease is usually self-limited

D. SalmonellosisCSalmonella typhimurium and others

1. Food-borne, particularly in poultry, eggs, and egg products; also in contaminated water

2. Food infection (bacteria must multiply and invade the intestinal mucosa)

3. Enterotoxin and cytotoxin destroy intestinal epithelial cells

4. Causes abdominal pain, cramps, diarrhea, and fever

5. Fluid loss can be a problem, particularly for children and elderly people

6. Treatment is fluid and electrolyte replacement

7. Controlled with good food preparation practices

E. ShigellosisCShigella spp

1. Shigellosis or bacterial dysentery is most prevalent in children 1 to 4 years old

2. Small infectious dose (10 to 100 bacteria)

3. It is a particular problem in day care centers and custodial institutions where there is crowding

4. They do not usually spread beyond the colon epithelium

5. Identification is based on biochemical characteristics and serology

6. Self-limiting in adults but may be fatal in children

7. Treatment is fluid and electrolyte replacement

8. Prevention is a matter of personal hygiene and a clean water supply

F. Staphylococcal food poisoningCStaphylococcus aureus

1. Caused by ingestion of improperly stored or prepared food in which the organism has grown

2. Organism produces several enterotoxins that cause severe abdominal pain, diarrhea, vomiting, and nausea

3. Symptoms come quickly (one to six hours) and leave quickly (24 hour)

4. Treatment is fluid and electrolyte replacement

G. Traveler=s Diarrhea and Escherichia coli Infections

1. Traveler=s diarrhea is caused by certain viruses, bacteria or protozoa normally absent from the traveler=s environment

2. E. coli is one of the major causative agents and may cause disease by a variety of mechanisms

3. Six categories or strains of diarrheagenic E. coli are now recognized

4. Enterotoxigenic E. coli (ETEC) produces two enterotoxins that are responsible for symptoms including hypersecretion of electrolytes and water into the intestinal lumen

5. Enteroinvasive E. coli (EIEC) multiplies within the intestinal epithelial cells; may also produce a cytotoxin and an enterotoxin

6. Enteropathogenic E. coli (EPEC) causes effacing lesions, destruction of brush border microvilli on intestinal epithelial cells

7. Enterohemorrhagic E. coli (EHEC) causes attaching-effacing lesions leading to hemorrhagic colitis; it also releases toxins that kill vascular epithelial cells; E. coli 0517:H7 is a major form of BHEC that has caused many outbreaks of hemorrhagic colitis in the U.S.

8. Enteroaggregative E. coli (EAggEC) forms clumps adhering to epithelial cells, toxins have not been identified but are suspected from the type of damage done

9. Diffusely adhering E. coli (DAEC) adheres in a uniform pattern to epithelial cells and is particularly problematic in immunologically naive or malnourished children

10. Diagnosis is based on past travel history and symptoms

11. Lab diagnosis is by isolation of the specific type of E. coli from feces and identification using DNA probes, determination of virulence factors, and the polymerase chain reaction

12. Treatment is electrolyte replacement plus antibiotics

13. Prevention and control involve avoiding contaminated food and water

H. Typhoid feverCSalmonella typhi

1. Caused by ingestion of food or water contaminated with human or animal feces

2. Symptoms are fever, headache, abdominal pain, and malaise that last several weeks

3. Treatment is with chloramphenicol, cephalosporin, or ampicillin

4. Control involves purification of drinking water, pasteurization of milk, preventing carriers from handling food, and complete patient isolation

5. A vaccine is available for high-risk individuals

V. Sepsis and Septic Shock

A. Cannot be categorized under a specific mode of transmission

B. Sepsis

1. Systemic response to a microbial infection

2. Manifested by fever or retrograde fever, heart rate > 90 beats per minute, respiratory rate > 20 breaths per minute, a pCO₂ < 32 mmHg, a leukocyte count > 12,000 cells per ml or < 4,000 cells per ml

C. Septic shock

1. Sepsis associated with severe hypotension (low blood pressure)

2. Gram-positive bacteria, fungi, and endotoxin-containing gram-negative bacteria can initiate the pathogenic cascade of sepsis leading to septic shock

3. Lipopolysaccharide (LPS), an integral component of the outer membrane of gram-negative bacteria has been implicated

D. Pathogenesis begins with localized proliferation of the microorganism

1. Bacteria may invade the bloodstream or may proliferate locally and release various products into the bloodstream

2. Products include structural components (endotoxins) and secreted exotoxins

3. These products stimulate the release of endogenous mediators of shock from plasma cells, monocytes, macrophages, endothelial cells, neutrophils, and their precursors

4. The endogenous mediators have profound effects on the heart, vasculature, and other body organs

5. Death ensues if one or more organ systems fail completely

E. Diagnosis is based primarily on symptoms

F. Early administration of antimicrobial therapy is important for effective management; broad spectrum antibiotics are used prior to culture results; this is followed by specifically tailored treatment

G. Monoclonal antibodies to endotoxin can attenuate adverse effects in shock patients

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