ANAEROBES AND PSEUDOMONAS OPPORTUNISTIC INFECTIONS
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 • Lecithinase (phospholipase, toxin) • C. perfringens enterotoxin • C. botulinum • Botulinum toxin • C. difficile • C. difficile enterotoxin • Pseudomonas aeruginosa • Pyocyanin • Fluorescein • Toxin A
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Obligate (strict) anaerobes
• • • • no oxidative phosphorylation fermentation killed by oxygen lack certain enzymes – superoxide dismutase * O2-+2H+ H2O2 – catalase * H2O2 H20 + O2 – peroxidase * H2O2 H20 /NAD to NADH
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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
Gram-negative rods: Bacteroides e.g. B. fragilis Fusobacterium, Porphyromonas, Prevotella 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
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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 • 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 • war • gas gangrene – swelling of tissues – gas release * fermentation products • wound contamination
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Pathogenesis
• tissue degrading enzymes – lecithinase [ toxin] – proteolytic enzymes – saccharolytic enzymes
• destruction of blood vessels • tissue necrosis • 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 • no 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
• After antibiotic use • intestinal normal flora – greatly decreased • colonization occurs • enterotoxin secreted • pseudomembanous colitis
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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) – fluorescein (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
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