Transcript Bacteria – Low GC Gram Positive

Chapter 23
Bacteria: The Low G + C
Gram Positives
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Low G + C Gram-Positive
The phylum Firmicutes divided into 3
classes
– Mollicutes
– Clostridia
– Bacilli
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Figure 23.1
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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
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Table 23.1
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Figure 23.3
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Growth of Mycoplasmas
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Figure 23.4
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More about Mycoplasma
• Genomes
– less than 1000 genes
– one of the smallest found in
procaryotes
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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
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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
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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.
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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
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Figure 23.6
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Class Clostridia
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Genus Clostridium
• Fermentative metabolism
– ferment amino acids using Stickland
reaction
• oxidation of one amino acid using another as
electron acceptor
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Important species of
Clostridium
• C. botulinum – food spoilage
(especially canned foods); botulism
• C. tetani – tetanus
• C. perfringens – gas gangrene
• C. acetobutylicum – manufacture of
butanol
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Figure 23.7
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Figure 23.8
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Class Bacilli
• Large variety of gram-positive
organisms
• Contains two orders, Bacillales
and Lactobacillales , 17 families
and over 70 genera
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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
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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
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Figure 23.9
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endospore
parasporal
body
Figure 23.10 (a)
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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
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Figure 23.11
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FamilyStaphylococcaceae
• Facultatively anaerobic, nonmotile,
gram-positive cocci
• Usually form irregular clusters
• Normally associated with warm
blooded animals in skin, skin glands
and mucous membranes
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Figure 23.13
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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
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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”
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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
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Order Lactobacillales
• Also called lactic acid bacteria
• Morphologically diverse
– nonsporing
– usually nonmotile
• Ferment sugars for energy
– lack cytochromes
– fastidious
• contains several important genera
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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)
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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
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Figure 23.14
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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
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Streptococci
• nonmotile
• facultative and
strict anaerobes
• homolactic
fermentation
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Lancefield grouping system –
based on polysaccharide and
techoic acid antigens in cell wall
or between cell wall and plasma
membrane
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
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Figure 23.17
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Enterococci and lactococci
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Figure 23.18
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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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