Anaerobes And Pseudomonas Opportunistic Infections

ANAEROBES AND PSEUDOMONAS OPPORTUNISTIC INFECTIONS

Faculty: Dr. Alvin Fox 1

MAJOR POINTS Overview of anaerobic bacteriology Anaerobic non-spore formers Anaerobic spore formers (clostridia) Pseudomonas (a strict aerobe) 2

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

• C. perfringens • Lecithinase (phospholipase, α toxin) • C. perfringens enterotoxin • C. botulinum • Botulinum toxin • C. difficile • C. difficile enterotoxin • Pseudomonas aeruginosa • Pyocyanin • Fluorescein • Toxin A 3

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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 4

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 . 11

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 15

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 18

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 [α toxin] – proteolytic enzymes – saccharolytic enzymes • destruction of blood vessels • tissue necrosis • anaerobic environment created • organism spreads 24

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 30

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) 36

PSEUDOMONAS AERUGINOSA

Gram negative rod 37

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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