ANAEROBES and Pseudomonas Lecture 39

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ANAEROBES and Pseudomonas Lecture 39
Faculty Dr. Alvin Fox
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MAJOR POINTS
Overview of anaerobic bacteriology
Anaerobic non-spore formers
Anaerobic spore formers (clostridia)
Pseudomonas (a strict aerobe)
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KEY WORDS

• Obligate anaerobes
• Strict anaerobes
• Polymicrobic (mixed) infection
• Spore formers
• Non-spore formers
• Bacteroides
• B. fragilis
• Clostridium tetani
• - tetanospasmin

• C. perfringens
• - a toxin (lecithinase phospholipase)
• C. perfringens
• - enterotoxin
• C. botulinum
• - botulinum toxin
• C. difficile
• - exotoxin A (cytotoxin)
• Pseudomonas aeruginosa
• - pyocyanin
• - pyroverdin
• - exotoxin A

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Obligate anaerobes

• no oxidative phosphorylation
• fermentation
• killed by oxygen
• lack certain enzymes
• superoxide dismutase
• O2-2H H2O2
• catalase
• H2O2 H20 O2
• peroxidase
• H2O2 NADH H 2H20 NAD

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Polymicrobic anaerobic infection

• Many species in human flora
• Many grow simultaneously - opportunistic
• conditions

• opportunistic growth
• injured tissue
• limited blood/O2
• no growth
• healthy tissues
• high O2 content

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Polymicrobic anaerobic infection

• Simultaneous infection with facultative
  anaerobe
• diminishes O2 supply further
• aids growth of obligate anaerobes

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Endogenous versus exogenous infection

• Two sources
• normal human flora
• endogenous
• environment (e.g. soil)
• exogenous

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Source of spore-formers and non-spore formers

• Spore-formers (clostridia)
• exotoxins
• common in the environment (e.g. soil)
• found in normal flora
• Non - spore-formers
• no exotoxins
• mostly normal flora

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Sites of anaerobes in normal flora

• intestine
• major site
• 95-99 total bacterial mass
• mouth
• genitourinary tract

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Bacteroides fragilis

• minor component of gut flora
• most common (strict) anaerobic infection after
  abdominal surgery

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• Enterobacteriaceae (facultative anaerobes)
• commonly cause disease
• low numbers gut flora
• Strict anaerobes
• much less commonly cause disease
• high numbers gut flora
• .

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Strict anaerobe infectious disease

• Sites throughout body
• Muscle, cutaneous/sub-cutaneous necrosis
• abscesses

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Problems in identification of anaerobic
infections

• air in sample (sampling, transportation)
• no growth
• identification takes several days or longer
• limiting usefulness
• often derived from normal flora
• sample contamination can confuse

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LABORATORY IDENTIFICATION

• BIOCHEMICAL KITS
• - e.g. substrate utilization
• GAS CHROMATOGRAPHY
• volatile fermentation products

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ANAEROBIC NON-SPORE-FORMERS OF CLINICAL
IMPORTANCE
Bacteroides e.g. B. fragilis Fusobacterium,
Porphyromonas, Prevotella
Gram-negative rods
Gram-positive rods Actinomyces,
Bifidobacterium, Eubacterium Lactobacillus,
Mobiluncus, Propionibacterium
Gram-positive cocci
Peptostreptococcus and Peptococcus
Gram-negative cocci Veillonella
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Bacteroides fragilis

• Major disease causing strict anaerobic
• non-spore-former

• Prominent capsule
• anti-phagocytic
• abscess formation

• Endotoxin
• low toxicity
• structure different than other lipolysaccharide
• beta lactamase

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ANAEROBIC SPORE-FORMERS (CLOSTRIDIA)

• Gram-positive rods
• human intestine
• soil

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Clostridium tetani
spore
vegetative
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Clostridium tetani

• Non-invasive

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Tetanospasmin

• disseminates systemically
• binds to ganglioside receptors
• inhibitory neurones in CNS, signal stopped
• muscles keep on working
• spastic (rigid) paralysis
• glycine, neurotransmitter

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A severe case of tetanus. muscles, back and
legs are rigid muscle spasms can break bones
can be fatal (e.g respiratory failure)
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Vaccination

• infant
• DPT (diptheria, pertussis, tetanus)
• tetanus extremely uncommon in US
• tetanus toxoid
• antigenic
• no exotoxic activity

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C. perfringens

• soil, fecal contamination
• especially in war
• gas gangrene
• - swelling of tissues
• - gas release (fermentation products)
• - tissue destruction (see next slide)

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a toxin

• tissue degrading enzymes
• a toxin (lecithinase, phospholipase)
• destruction of blood vessels
• myonecrosis
• anaerobic environment created
• organism spreads

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Without treatment death occurs within 2 days

• effective antibiotic therapy
• debridement
• anti-toxin
• amputation death is rare

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Laboratory identification

• lecithinase production

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Food poisoning

• enterotoxin producing strains

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C. botulinum
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Botulism

• food poisoning
• rare
• fatal
• germination of spore
• inadequately sterilized canned food
• home
• not an infection

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Botulinum toxin

• binds peripheral nerve receptors
• acetylcholine neurotransmitter
• inhibits nerve impulses
• flaccid paralysis
• death
• respiratory
• cardiac failure

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Infection with C. botulinum

• Neonatal botulism
• uncommon
• the predominant form of botulism
• colonization occurs
• limited normal flora to compete
• unlike adult

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Wounds

• extremely rare
• an infection

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Botulinum toxin

• Bioterrorism
• not an infection
• resembles a chemical attack

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Treatment

• anti-toxin
• antibiotic therapy (if infection)

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C. difficile

• pseudomembanous colitis
• after antibiotic use
• intestinal normal flora
• greatly decreased
• colonization occurs
• exotoxin A (enterotoxin, cytoxin)
• - most potent
• exotoxin B
• - secondary (also a cytoxin)

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Therapy

• discontinuation of initial antibiotic (e.g.
  ampicillin)
• specific antibiotic therapy (e.g. vancomycin)

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PSEUDOMONAS AERUGINOSA
Gram negative rod
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Pseudomonas

• Aerobic
• Gram-negative rod
• majority of human infections
• P. aeruginosa

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Common in the environment

• water
• air
• soil

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P. aeruginosa and compromised host

• Burns and wounds
• destruction of blood vessels
• phagocyte access limited
• cancer
• cytotoxic drugs
• destroy the immune system
• cystic fibrosis
• altered respiratory epithelium
• pneumonia
• .

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Identification

• Pigments
• pyocyanin (blue-green)
• pyoverdin (green-yellow, fluorescent)
• biochemical reactions
• cultures have fruity smell

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Pathogenesis

• Slime layer is anti-phagocytic
• Toxin A - ADP ribosylates EF2
• similar to diphtheria toxin