Anaerobes and Pseudomonas Opportunistic Infections Fox

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,  toxin) • C. perfringens enterotoxin • C. botulinum • Botulinum toxin • C. difficile • C. difficile enterotoxin • Pseudomonas aeruginosa • Pyocyanin • Fluorescein • Toxin A 3 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 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 5 Polymicrobic anaerobic infection • Simultaneous infection with facultative anaerobe –diminishes O2 supply further – aids growth of obligate anaerobes 6 Endogenous versus exogenous infection • Two sources – normal human flora • endogenous – environment (e.g. soil) • exogenous 7 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 8 Sites of anaerobes in normal flora • intestine – major site – 95-99% total bacterial mass • mouth • genitourinary tract 9 Bacteroides fragilis • minor component of gut flora • most common (strict) anaerobic infection after abdominal surgery 10 • 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 12 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 13 LABORATORY IDENTIFICATION • BIOCHEMICAL KITS - e.g. substrate utilization • GAS CHROMATOGRAPHY – volatile fermentation products 14 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 16 ANAEROBIC SPORE-FORMERS (CLOSTRIDIA) • Gram-positive rods – human intestine – soil 17 Clostridium tetani spore vegetative 18 Clostridium tetani • Non-invasive 19 Tetanospasmin • disseminates systemically • binds to ganglioside receptors – inhibitory neurones in CNS • muscles keep on working • spastic (rigid) paralysis • glycine – neurotransmitter 20 A severe case of tetanus. muscles, back and legs are rigid muscle spasms can break bones can be fatal (e.g respiratory failure) 21 Vaccination • infant • DPT (diptheria, pertussis, tetanus) • tetanus extremely uncommon in US • tetanus toxoid – antigenic – no exotoxic activity 22 C. perfringens • soil, fecal contamination • war • gas gangrene – swelling of tissues – gas release * fermentation products • wound contamination 23 Pathogenesis • tissue degrading enzymes – lecithinase [ 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 25 Laboratory identification • lecithinase production 26 Food poisoning • enterotoxin producing strains 27 C. botulinum 28 Botulism • food poisoning – rare – fatal • germination of spore • inadequately sterilized canned food – home • not an infection 29 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 31 Wounds – extremely rare – an infection 32 Botulinum toxin • Bioterrorism – not an infection – resembles a chemical attack 33 Treatment • anti-toxin • antibiotic therapy (if infection) 34 C. difficile • After antibiotic use • intestinal normal flora – greatly decreased • colonization occurs • enterotoxin secreted • pseudomembanous colitis 35 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 38 Common in the environment • water • air • soil 39 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 . 40 Identification • Pigments – pyocyanin (blue-green) – fluorescein (green-yellow, fluorescent) • biochemical reactions • cultures have fruity smell 41 Pathogenesis • Slime layer is anti-phagocytic • Toxin A - ADP ribosylates EF2 – similar to diphtheria toxin 42