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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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major points
MAJOR POINTS

Overview of anaerobic bacteriology

Anaerobic non-sporeformers

Anaerobic spore formers

(clostridia)

Pseudomonas (a strict aerobe)

key words
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
obligate anaerobes
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
polymicrobic anaerobic infection
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
slide6

Polymicrobic anaerobic infection

  • Simultaneous infection with facultative anaerobe
    • diminishes O2 supply further
    • aids growth of obligate anaerobes
endogenous versus exogenous infection
Endogenous versus exogenous infection
  • Two sources
    • normal human flora
      • endogenous
    • environment (e.g. soil)
      • exogenous
source of spore formers and non spore formers
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
sites of anaerobes in normal flora
Sites of anaerobes in normal flora
  • intestine
    • major site
    • 95-99% total bacterial mass
  • mouth
  • genitourinary tract
bacteroides fragilis
Bacteroides fragilis
  • minor component of gut flora
  • most common (strict) anaerobic infection after abdominal surgery
slide11

Enterobacteriaceae (facultative anaerobes)

    • commonly cause disease
    • low numbers gut flora
  • Strict anaerobes
    • much less commonly cause disease
    • high numbers gut flora

.

strict anaerobe infectious disease
Strict anaerobe infectious disease
  • Sites throughout body
  • Muscle, cutaneous/sub-cutaneous necrosis
  • abscesses
slide13

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
laboratory identification
LABORATORY IDENTIFICATION
  • BIOCHEMICAL KITS

- e.g. substrate utilization

  • GAS CHROMATOGRAPHY
    • volatile fermentation products
anaerobic non spore formers of clinical importance
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

bacteroides fragilis16
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
anaerobic spore formers clostridia
ANAEROBIC SPORE-FORMERS (CLOSTRIDIA)
  • Gram-positive rods
    • human intestine
    • soil
clostridium tetani
Clostridium tetani

spore

vegetative

clostridium tetani19
Clostridium tetani
  • Non-invasive
tetanospasmin
Tetanospasmin
  • disseminates systemically
  • binds to ganglioside receptors
    • inhibitory neurones in CNS, signal stopped
  • muscles keep on working
  • spastic (rigid) paralysis
  • glycine, neurotransmitter
slide21

A severe case of tetanus.

muscles, back and legs are rigid

muscle spasms can break bones

can be fatal(e.g respiratory failure)

slide22

Vaccination

  • infant
  • DPT (diptheria, pertussis, tetanus)
  • tetanus extremely uncommon in US
  • tetanus toxoid
        • antigenic
        • no exotoxic activity
c perfringens
C. perfringens
  • soil, fecal contamination
  • war
  • gas gangrene
    • swelling of tissues
    • gas release
      • fermentation products
  • wound contamination
slide24

Pathogenesis

  • tissue degrading enzymes
    • lecithinase(α toxin)
    • proteolytic enzymes
    • saccharolytic enzymes
  • destruction of blood vessels
  • tissue necrosis
  • anaerobic environment created
  • organism spreads
slide25

Without treatment death

occurs within 2 days

  • effective antibiotic therapy
  • debridement
  • anti-toxin
  • amputation & death is rare
slide26

Laboratory identification

  • lecithinase production
food poisoning
Food poisoning
  • enterotoxin producing strains
botulism
Botulism
  • food poisoning
    • rare
    • fatal
  • germination of spore
  • inadequately sterilized canned food
    • home
  • not an infection
botulinum toxin
Botulinum toxin
  • binds peripheral nerve receptors
    • acetylcholine neurotransmitter
  • inhibits nerve impulses
  • flaccid paralysis
  • death
    • respiratory
    • cardiac failure
infection with c botulinum
Infection with C. botulinum
  • Neonatal botulism
    • uncommon
    • the predominant form of botulism
    • colonization occurs
      • limited normal flora to compete
      • unlike adult
wounds
Wounds
  • extremely rare
  • an infection
botulinum toxin33
Botulinum toxin
  • Bioterrorism
    • not an infection
    • resembles a chemical attack
slide34

Treatment

  • anti-toxin
  • antibiotic therapy (if infection)
c difficile
C. difficile
  • After antibiotic use
  • intestinal normal flora
    • greatly decreased
  • colonization occurs
  • exotoxin A (enterotoxin)
  • exotoxin B (cytoxin)
  • pseudomembanous colitis
therapy
Therapy
  • discontinuation of initial antibiotic (e.g. ampicillin)
  • specific antibiotic therapy (e.g. vancomycin)
pseudomonas aeruginosa
PSEUDOMONAS AERUGINOSA

Note

pairs

Gram negative

rod

pseudomonas
Pseudomonas
  • Aerobic
  • Gram-negative rod
  • majority of human infections
    • P. aeruginosa
slide40

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
  • .
slide41

Identification

  • Pigments
    • pyocyanin (blue-green)
    • pyoverdin(green-yellow, fluorescent)
  • biochemical reactions
  • cultures have fruity smell
slide42

Pathogenesis

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