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Flashcards in Anaerobic Bacteria Deck (17)

Common sources of anaerobic pathogen-normal flora

Normal flora:
-escape from normal compartment (Actinomyces, B corrodens, P. melaninogenica: mouse; B fragilis: colon and vagina
-establish abscesses
-abscess fills with bacteria and dead neutrophils, swells and becomes painful


Common source of Pathogen- soil (spores)

-route of entry A- spores enter through wounds, germinate, and produce exotoxins- C. tetani, C. perfringens in gas gangre, C. botulinum- in wound botulism


Common source of pathogen- soil (in food)

-route of entry B- spores germinate in vacuum packed foods
-C. perfringens in food poisoning: bacteria briefly survive in gut and release enteroxtoxin
-C. botulism infant botulism: bacteria briefly survive in gut and release neurotoxin
-C. botulinum in foodborne botulism- bacteria do not survive the gut, but have already filled food with neurotoxin


Handling anaerobes in the laboratory

-sample must be handled anaerobically and labeled as such
-standard clinical labs are anaerobic culture, gram stain, gas chromatography


Anaerobic Liquid Culture

-innoculate test tube of media
-add a reducing agent like thioglycolate to eliminate dissolved oxygen
-fill completely, stopper tightly and incubate without shaking
-strict aerobes on top- pseudomonas
-strict anaerobe on bottom- clostridum
-facultative anaerobe- E. coli


Anaerobic culture streaking plates

-quickly streak onto agar media with usual benchtop sterile technique
-place plates in anaerobic culture jar
-add a chemical system to remove oxygen from the jar's atmosphere and color indicate successful removed (Gas Pak)
-Airtight seal
-place whole jar in incubator for 48h
-note that colonies will die very shortly after removal from jar unless using a glovebox


Identifying Anaerobes

-gram stain
-chemical testing (ability to ferment, hydrolize various macromolecules
-gas chromatography


Anaerobic Infections: treatments

1) if abscess- surgical care: drain, debride
2) If toxigenic: antitoxin
3) Antibiotics: penicillin G, cefoxitin, chloramphenicol, clindamycin, metronidazole: specific for anaerobic bacteria, some protozoans


Some anaerobic bacteria

-Clostridium- gram +, rod, spores
-Bacteroides- gram -, rod, no spores
-Prevotella- gram -, rod, no spores
-Actinomyces- gram +, long filamentous rod, no spores


Some anerobic bacteria and their reservoirs and primary virulence factors

C. tetani- soil, tetanus, tetanospasmin
C. botulinum- soil, botulism, botulinum toxin
C. perfringens- soil, Gas Gangrene, Many tissue degrading enzymes
C. perfringens- soil, food poisoning, enterotoxin
C. difficile- normal flora, pseudomembranous colitis, exotoxins A and B
GNAB- Normal flora, Abscesses, a few tissue-degrading enzymes, capsule
Actiomyces spp- normal flora, Actinomycosis (abscess)


Clostrudium tetani

-spores are environmental: soil, dust, manure, some human skin and GI
-gram +
-transmitted to humans by soil contamination of wounds: splinters, thorns, punctures, IV drugs, septic surgery, septic handling of umbilical cord
-insertion beneath skin surface limits air contact
-spores germinate
-vegetative cells release exotoxin tetanospasmin



-50kDa small subunit travels 2-14 days to spinal cord
-acts as protease, cleaves synaptobrevin in inhibitory motor nerves of the CNS
-without synaptobrevin, vesicles containing GABA and glycine cannot be released from affected neuron
-loss of central inhibitory activity on motor and autonomic neurons


Generalized tetanus

-bacteria form a locus of infection
-exotoxin tetanospasmin enters bloodstream
-full-body symptoms cause morbidity
->50% untreated mortality from respiratory failure
-21-31% treated mortality


C. tetani prevention

-universal vaccination with tetanus toxoid( formaldehyde- treated toxin) in childhood (DTaP) according to standard schedule, adults get booster every 10 years


C. difficile

-gram + spore forming rod
-causes pseudomembranous colitis= C. difficile- associated diarrhea (CDAD)= antibiotic-associated colitis= C. difficile colitis
-normal gut flora for 3% of general pop, 30% of hospitalized
-fecal oral- especially nosocomial from spores on hospital instruments or on hands of health care workers


Pathogenesis of C. difficule

-recent course of antibiotics or cancer chemotherapeutics suppresses other normal flora, allows C. difficile to overgrow
-germinating cells release Exotoxin A, which disrupts tight junctions, causing intestinal swelling and inflammation
-exotoxin B is the major toxin, disrupts the cytoskeleton by depolymerizing actin, kills the surrounding cells
-a more virulent and drug-resistant strain of C. difficile emerged in 2001-2002; cases doubled 2000-2003 and have continued to rise since
-mortalitiy has increased from 6%


C. difficile: diagnosis and treatment

-on sigmoidoscopy, patches of dead and dying cells appear as yellow-white plaques (pseudomembranes)
-withdraw initial antibiotic- cures 20%
-oral metronidazole or vancomycin
-surgical resection or removal of the colon may be required
-toxic megacolon or colonic perforation may occur