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Chapter 23

Chapter 23. Bacteria: The Low G + C Gram Positives. Low G + C Gram-Positive. The phylum Firmicutes divided into 3 classes Mollicutes Clostridia Bacilli. Figure 23.1. Class Mollicutes (The Mycoplasmas ). Lack cell walls and are pleomorphic cannot synthesize peptidoglycan precursors

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Chapter 23

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  1. Chapter 23 Bacteria: The Low G + C Gram Positives

  2. Low G + C Gram-Positive The phylum Firmicutes divided into 3 classes • Mollicutes • Clostridia • Bacilli

  3. Figure 23.1

  4. Class Mollicutes (The Mycoplasmas) • Lack cell walls and are pleomorphic • cannot synthesize peptidoglycan precursors • penicillin resistant • sterols may stabilize plasma membrane • most nonmotile; some have gliding motility • smallest bacteria capable of self-reproduction

  5. Table 23.1

  6. Figure 23.3

  7. Growth of Mycoplasmas

  8. Figure 23.4

  9. More about Mycoplasma • Genomes • less than 1000 genes • one of the smallest found in procaryotes

  10. Metabolism of Mycoplasmas • Chemoorganotrophs • some produce ATP by glycolysis and lactic acid fermentation • some catabolize amino acids and urea • some have functional pentose phosphate pathway • none have complete TCA cycle • deficient in a number of biosynthetic pathways

  11. Important pathogens • Mycoplasma mycoides – bovine pleuropneumonia in cattle • Mycoplasma gallisepticum – chronic respiratory disease in chickens • Mycoplasma hyopneumoniae – pneumonia in swine • Mycoplasma pneumoniae – primary atypical pneumonia in humans • Ureaplasma urealyticum – premature birth, neonatal meningitis and pneumonia • spiroplasmas – pathogenic in insects, ticks, and a variety of plants

  12. Bacillus and Clostridium • Production of endospores is a hallmark of the key genera Bacillus and Clostridium. • Gram-positive Bacteria are major agents for the degradation of organic matter in soil, and a few species are pathogenic.

  13. Endospores • Have a complex structure containing a coat, cortex, and inner spore membrane surrounding the protoplast • Dipicolinic acid is present • Heat resistant • dormant and viable for long periods of time

  14. Figure 23.6

  15. Class Clostridia

  16. Genus Clostridium • Fermentative metabolism • ferment amino acids using Stickland reaction • oxidation of one amino acid using another as electron acceptor

  17. Important species of Clostridium • C. botulinum – food spoilage (especially canned foods); botulism • C. tetani – tetanus • C. perfringens – gas gangrene • C. acetobutylicum – manufacture of butanol

  18. Figure 23.7

  19. Figure 23.8

  20. Class Bacilli • Large variety of gram-positive organisms • Contains two orders, Bacillales and Lactobacillales , 17 families and over 70 genera

  21. Bacillus subtilis • Used as model organism for cellular differentiation, division and other processes • Its genome was one of first to be sequenced • has families of genes expanded by gene duplication • 10 integrated prophages or remnants of prophages • Various species produce antibiotics

  22. Other important species of Bacillus • B. cereus – food poisoning • B. anthracis – anthrax • B. thuringiensis and B. sphaericus – used as insecticide • parasporal body – solid protein crystal that contains toxin

  23. Figure 23.9

  24. endospore parasporal body Figure 23.10 (a)

  25. Genus Thermoactinomyces • Historically classified as actinomycete • More recently, phylogenetic analysis places it with low G+C microbes in order Bacillales, family Thermoactinomycetaceae • Commonly found in high temperature environments such as composts

  26. Figure 23.11

  27. FamilyStaphylococcaceae • Facultatively anaerobic, nonmotile, gram-positive cocci • Usually form irregular clusters • Normally associated with warm blooded animals in skin, skin glands and mucous membranes

  28. Figure 23.13

  29. Pathogenic Staphylococcus • Staphylococcus epidermidis • common skin resident • sometimes responsible for endocarditis and for infections of patients with lowered resistance • e.g., wound infections, surgical infections, and urinary tract infections

  30. Antibiotic Resistant Staphylococci • Resistance to methicillin • Methicillin-Resistant Staphylococcus aureus (MRSA) • obtained from genetic elements received from other organisms • Resistance to vancomycin, the “drug of last resort”

  31. Staphylococcus aureus • Produces the virulence factor coagulase • causes blood plasma to clot • Produces a-hemolysin • toxin which lyses cells • major cause of food poisoning • recently >1,000 school children in Texas had staphylococcal food poisoning caused by eating improperly handled chicken • Found on nasal membranes and skin, and in gastrointestinal and urinary tracts

  32. Order Lactobacillales • Also called lactic acid bacteria • Morphologically diverse • nonsporing • usually nonmotile • Ferment sugars for energy • lack cytochromes • fastidious • contains several important genera

  33. Order Lactobacillales • Largest genus - Lactobacillus • grow optimally in slightly acidic conditions (pH 4.5 to 6.4) • carry out either homolactic fermentation (via glycolytic pathway) or heterolactic fermentation (via pentose phosphate pathway)

  34. Genus Lactobacillus • Widely distributed in nature • on plant surfaces • in dairy products, meat, water, sewage, beer, fruits, and other materials • normal flora of mouth, intestinal tract, and vagina • usually not pathogenic

  35. Figure 23.14

  36. Importance of lactobacilli • Fermented vegetable products (sauerkraut, pickles, and silage) • Fermented beverages (beer, wine, juices) • Sour dough bread • Swiss cheese and other hard cheeses • yogurt • Sausages • spoilage of beer, milk, and meat

  37. Streptococci Lancefield grouping system – based on polysaccharide and techoic acid antigens in cell wall or between cell wall and plasma membrane • nonmotile • facultative and strict anaerobes • homolactic fermentation

  38. a-hemolysis • incomplete lysis of red blood cells • seen as greenish zone around colony on blood agar b-hemolysis • complete lysis of red blood cells • seen as clear zone around colony on blood agar Table 23.5

  39. Figure 23.17

  40. Enterococci and lactococci

  41. Figure 23.18

  42. Important streptococci, enterococci, and lactococci • Streptococcus pyogenes – streptococcal sore throat, acute glomerulonephritis, and rheumatic fever • Streptococcus pneumoniae – lobar pneumonia and otitis media • Streptococcus mutans – dental caries • Enterococcus faecalis – opportunistic pathogen (urinary tract infections and endocarditis) • Lactococcus lactis – production of buttermilk and cheese

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