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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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• 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.

Bacillus and Clostridium

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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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parasporalbody

endospore

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 -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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• nonmotile• facultative andstrict anaerobes• homolacticfermentation

Lancefield grouping system – based on polysaccharide andtechoic acid antigens in cell wallor between cell wall and plasmamembrane

Streptococci

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-hemolysis– incomplete lysis of red blood cells– seen as greenish zone around colony on blood agar

-hemolysis– complete lysis of red blood cells– seen as clear zone around colony on blood agar

Table 23.5

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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