1

2
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

6
Table 23.1

7
Figure 23.3

8
Growth of Mycoplasmas

9
Figure 23.4

10
•
Genomes
– less than 1000 genes
– one of the smallest found in procaryotes

11
•
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

•
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

14
•
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

Figure 23.6
15

16

17
•
Fermentative metabolism
– ferment amino acids using Stickland reaction
• oxidation of one amino acid using another as electron acceptor

18
•
C. botulinum – food spoilage
(especially canned foods); botulism
•
C. tetani – tetanus
•
C. perfringens – gas gangrene
•
C. acetobutylicum – manufacture of butanol

Figure 23.7
19

Figure 23.8
20

21

22
•
Large variety of gram-positive organisms
•
Contains two orders, Bacillales and Lactobacillales , 17 families and over 70 genera

23
•
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

24
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

Figure 23.9
25

endospore
Figure 23.10 (a)
26 parasporal body

27
•
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

Figure 23.11
28

29
•
Facultatively anaerobic, nonmotile, gram-positive cocci
•
Usually form irregular clusters
•
Normally associated with warm blooded animals in skin, skin glands and mucous membranes

Figure 23.13
30

31
•
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

32
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”

33
•
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

34
•
Also called lactic acid bacteria
•
Morphologically diverse
– nonsporing
– usually nonmotile
•
Ferment sugars for energy
– lack cytochromes
– fastidious
• contains several important genera

•
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)
35

36
•
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

Figure 23.14
37

38
•
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

• nonmotile
• facultative and strict anaerobes
• homolactic fermentation
39
Lancefield grouping system
– based on polysaccharide and techoic acid antigens in cell wall or between cell wall and plasma membrane

40
Table 23.5
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

Figure 23.17
41

42

Figure 23.18
43

44
• 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