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General Information

  • Strict anareobes are poisoned by any amount of oxygen
  • If it is aerobic and sporulating, it is a bacteria
  • If it is anaerobic and sporulating - it is a clostridia
  • Nothing else in the bacterial world forms spores
  • Clue to anaerobic infections: foul smelling discharges and free gas in tissues
  • Anaerobic bacteria rarely appear in isolation
  • Originally the world was anaerobic
  • Anaerobes are difficult to identify in the laboratory since they are usually found in abscesses, etc
  • Culturing anaerobes is pointless because they are always present
  • It would take a large laboratory nearly 1.5 years to identify all the anaerobes from a mucosal swab taken from the mouth

Common Anaerobes


  • produces β-lactimase enzyme which confers resistance against penicillin
  • commonly found in the gastrointestinal tract


  • trivial and unimportant organism
  • Common contaminant in blood cultures post 4-5 days
  • Often found on skin



  • important
  • nasty, highly important spore-forming human pathogen


Fournier's Gangrene

  • Caused by Bacteroides fragilis
  • a terrible disease
  • need to do a broad excision mid-thigh to umbilicus
  • More info: Harrison's Online


  • Affects all muscles spastically (spastic paralysis)
  • Called lockjaw because cranial nerves are the shortest nerves in the body, so they are affected first
  • First sign of tetanus is Risus sardonicus (sardonic smile)
  • Often, farmers present with no tetanus shot; they've stuck a nail in their foot, contaminated with soil
  • This usually accounts for a few cases a year
  • More info: Harrison's Online: Tetanus