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ANAEROBES and Pseudomonas Lecture 47

ANAEROBES and Pseudomonas Lecture 47. Faculty: Dr. Alvin Fox. MAJOR POINTS . Overview of anaerobic bacteriology. Anaerobic non-spore formers. Anaerobic spore formers (clostridia). Pseudomonas (a strict aerobe). Obligate anaerobes Strict anaerobes

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ANAEROBES and Pseudomonas Lecture 47

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  1. ANAEROBES and Pseudomonas Lecture 47 Faculty: Dr. Alvin Fox

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

  3. Obligate anaerobes Strict anaerobes Polymicrobic (mixed) infection Spore formers Non-spore formers Bacteroides B. fragilis Clostridium tetani - tetanospasmin C. perfringens - lecithinase (phospholipase, αtoxin) C. perfringens - enterotoxin C. botulinum - botulinum toxin C. difficile - exotoxin A (enterotoxin) - exotoxin B (cytotoxin) Pseudomonas aeruginosa - pyocyanin - pyroverdin - exotoxin A KEY WORDS

  4. 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

  5. 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

  6. Polymicrobic anaerobic infection • Simultaneous infection with facultative anaerobe • diminishes O2 supply further • aids growth of obligate anaerobes

  7. Endogenous versus exogenous infection • Two sources • normal human flora • endogenous • environment (e.g. soil) • exogenous

  8. 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

  9. Sites of anaerobes in normal flora • intestine • major site • 95-99% total bacterial mass • mouth • genitourinary tract

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

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

  12. Strict anaerobe infectious disease • Sites throughout body • Muscle, cutaneous/sub-cutaneous necrosis • abscesses

  13. 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

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

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

  16. 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

  17. ANAEROBIC SPORE-FORMERS (CLOSTRIDIA) • Gram-positive rods • human intestine • soil

  18. Clostridium tetani spore vegetative

  19. Clostridium tetani • Non-invasive

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

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

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

  23. C. perfringens • soil, fecal contamination • war • gas gangrene • swelling of tissues • gas release • fermentation products • wound contamination

  24. Pathogenesis • tissue degrading enzymes • lecithinase(α toxin) • proteolytic enzymes • saccharolytic enzymes • destruction of blood vessels • tissue necrosis • anaerobic environment created • organism spreads

  25. Without treatment death occurs within 2 days • effective antibiotic therapy • debridement • anti-toxin • amputation & death is rare

  26. Laboratory identification • lecithinase production

  27. Food poisoning • enterotoxin producing strains

  28. C. botulinum

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

  30. Botulinum toxin • binds peripheral nerve receptors • acetylcholine neurotransmitter • inhibits nerve impulses • flaccid paralysis • death • respiratory • cardiac failure

  31. Infection with C. botulinum • Neonatal botulism • uncommon • the predominant form of botulism • colonization occurs • limited normal flora to compete • unlike adult

  32. Wounds • extremely rare • an infection

  33. Botulinum toxin • Bioterrorism • not an infection • resembles a chemical attack

  34. Treatment • anti-toxin • antibiotic therapy (if infection)

  35. C. difficile • After antibiotic use • intestinal normal flora • greatly decreased • colonization occurs • exotoxin A (enterotoxin) • exotoxin B (cytoxin) • pseudomembanous colitis

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

  37. PSEUDOMONAS AERUGINOSA Note pairs Gram negative rod

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

  39. Common in the environment • water • air • soil

  40. 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 • .

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

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

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