This chapter describes the different approaches to gram-positive organisms taken by the 1^st and 2^nd editions of Bergey's Manual and then focuses on the mycoplasmas, Clostridium and its relatives, and the bacilli and lactobacilli.

After reading this chapter you should be able to:

• discuss the differences in classification of gram-positives that is used in the 1^st and 2^nd editions of Bergey's Manual
• discuss the variation in peptidoglycan structure that is useful in identifying specific groups
• discuss the various roles of these organisms; harmless, free-living saprophytes, pathogens, importance in the food and dairy industry

1. Class Mollicutes (The Mycoplasmas)

1. The new edition will have one order and three families
2. Mycoplasmas lack cell walls and cannot synthesize peptidoglycan precursors

1. Penicillin resistant
2. Susceptible to lysis by osmotic shock and detergent treatment

1. Smallest bacteria capable of self-reproduction
2. Most are nonmotile but some can glide along liquid-covered surfaces
3. Most species require sterols (unusual for bacteria)
4. Usually facultative anaerobes but a few are strict anaerobes
5. G + C content ranges from 23% to 41%
6. Can be saprophytes, commensals or parasites
7. Recently, the complete genome of M. genitalium has been sequenced
8. Metabolism is not particularly unusual although they are deficient in several biosynthetic pathways
9. Widespread - can be isolated from plants, animals, the soil and even compost piles
10. Serious contaminant of mammalian cell cultures; difficult to detect; difficult to eliminate
11. In animals they colonize mucous membranes and joints and are often are associated with diseases of the respiratory and urogenital tracts
12. Pathogenic species include:

1. M. mycoides - bovine pleuropneumonia in cattle
2. M. gallisepticum - chronic respiratory disease in chickens
3. M. pneumoniae - primary atypical pneumonia in humans
4. M. hominis and Ureaplasma urealyticum - pathogenic in humans
5. Spiroplasmas - pathogenic in insects, ticks, and a variety of plants

1. Low G + C Gram-Positive Bacteria in Bergey's Manual

1. First edition treats low G + C gram-positives phenotypically

1. Classified on the basis of cell shape, clustering and arrangement of cells, presence or

absence of endospores, oxygen relationships, fermentation patterns, peptidoglycan

chemistry, etc.

2. Peptidoglycan structure varies considerably

1. a. Some contain meso-diaminopimelic acid cross-linked through its free amino group to

1. Others contain lysine cross-linked by interpeptide bridges
2. Others contain L,L-diaminopimelic acid and have one glycine as the interpeptide bridge
3. Pathogenic corynebacteria use ornithine to cross-link between positions 2 and 4 of the peptide chains rather than positions 3 and 4 as used by the other forms
4. Other cross-links and differences in cross-link frequency also contribute to variation in structure
5. These variations are characteristic of particular groups and are therefore taxonomically useful

1. Bacterial endospores are complex structures that allow survival under adverse conditions

1. Recently viable endospores have been found that may be over 25 million years old
2. Sporeformers are distributed widely but found mainly in soil

1. Second edition takes a phylogenetic approach dividing the low G + C gram-positives into two

1. The Clostridia and Relatives

1. Contains one class with two orders and at least eight families
2. The largest genus is Clostridium

1. Obligate anaerobes, sporeformers, do not carry out dissimilatory sulfate reduction
2. Over 100 species in distinct phylogenetic clusters
3. Responsible for many cases of food spoilage, even in canned foods (e.g., C. botulinum)
4. Other major disease causing clostridia include:

1. C. perfringens - gas gangrene
2. C. tetani - tetanus

1. Some are of industrial value (e.g., C. acetobutylicum - used to manufacture butanol)

1. Epulopiscium - giant bacteria
2. Desulfotomaculum

1. Anaerobic, endospore-forming genus that reduces sulfate and sulfite to hydrogen sulfide

during anaerobic respiration

2. Stains gram-negative (placed with gram-negatives in 1^st edition) but actually has a gram-

1. Heliobacterium and Heliophilum - are photosynthetic using bacteriochlorophyll g, but no

F. Veillonella

1. Anaerobic, chemoheterotrophic cocci with complex nutritional requirements
2. Parasites of homeothermic animals
3. Part of the normal microflora of the mouth, the gastrointestinal tract, and urogenital tract of humans and other animals
4. Classified with gram-negatives in the 1^st edition but are actually more closely related to low G + C gram-positives

1. The Bacilli and Lactobacilli

1. Order Bacilliales

1. Largest genus in the order
2. Gram-positive, endospore-forming, chemoheterotrophic rods
3. Usually motile with peritrichous flagella
4. Usually aerobic, sometimes facultative, and catalase positive
5. Some new genera have been created: Alicyclobacillus and Paenibacillus
6. Many species are of considerable importance

1. Some produce antibiotics such as bacitracin, gramicidin and polymyxin
2. B. cereus causes food poisoning
3. B. anthracis causes anthrax
4. B. thuringiensis and B. sphaericus are used as insecticides

1. Thermophilic; forms single spores on both its aerial and substrate mycelia
2. Commonly found in damp haystacks, compost piles, and other high-temperature habitats
3. Very heat-resistant endospores - can survive 90° C for 30 minutes
4. T. vulgaris - causative agent for farmer's lung disease, an allergic respiratory disease in agricultural workers

1. Caryophanon - strict aerobe, catalase positive, motile by peritrichous flagella
2. Staphylococcus

1. Facultatively anaerobic, catalase positive, oxidase negative
2. Ferment glucose anaerobically
3. Normally associated with skin, skin glands, and mucous membranes
4. S. epidermidis - skin resistant; sometimes responsible for endocarditis and for infections of patients with lowered resistance (wound infections, surgical infections, and urinary tract infections)
5. S. aureus - found on nasal membranes, skin, and in the gastrointestinal and urinary tracts; associated with boils, abscesses, wound infections, pneumonia, toxic shock syndrome and food poisoning; produces coagulase which causes blood to clot

1. Order Lactobacilliales

1. Largest genus is Lactobacillus with nearly 80 species
2. Can be rods, and sometimes coccobacilli, that lack catalase and cytochromes, are usually facultative or microaerophilic, produce lactic acid, and have complex nutritional requirements
3. Lactobacillus

1. Can carry out heterolactic or homolactic acid fermentation
2. Grow optimally between pH 4.5 and pH 6.4
3. Found on plant surfaces and in dairy products, meat, water, sewage, beer, fruits, and many other materials
4. Normal microflora of mouth, intestinal tract, and vagina; usually not pathogenic
5. Used in the production of fermented vegetable foods, beverages, sour dough, hard cheeses, yogurt, and sausages
6. Responsible for spoilage of beer, milk, and meat

1. a. Facultatively anaerobic; elongated or elliptical shape; clustered in pairs or chains
2. b. Lack catalase or cytochromes; heterolactic fermentation
3. c. Important in wine production, fermentation of vegetables such as cabbage and
4. cucumbers, manufacture of buttermilk, butter and cheese; tolerate high sugar concentrations and, therefore, grow in heavy syrup

5. Streptococcus

5. a. Pairs or chains in liquid media; does not form endospores, nonmotile
6. b. Homolactic fermentation; produces lactic acid but no gas
7. c. Most are facultative anaerobes; a few are obligate anaerobes
8. d. Distinguished by hemolysis reactions
9. (1) a -hemolysis - incomplete with greenish zone
10. (2) b -hemolysis - complete with clear zone - no greening

1. Also distinguished serologically and by a variety of biochemical and physiological

tests

2. Many bacteria originally in this genus have been moved to the genus Enterococcus

(18 species) or to the genus Lactococcus (8 species)

3. Species of practical importance include:

1. S. pyogenes - causes streptococcal sore throat, acute glomerulonephritis and rheumatic fever
2. S. pneumonia - causes lobar pneumonia
3. S. mutans - associated with dental caries
4. E. faecalis - opportunistic pathogen that can cause urinary tract infections and endocarditis
5. L. Lactis - used in the production of buttermilk and cheese

1. Listeria - aerobic or facultative, catalase positive, peritrichously flagellated; L.