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Bacillus cereus

Cell Wall: Gram Positive Shape: Spore-forming Rod
Metabolism: Obligate Aerobe
Virulence Factors
  • Exotoxins
    • Heat-labile Enterotoxin: Similar mechanism of action as that of V. Cholera toxin and requires 12-24hrs to cause infectious diarrhea
    • Heat-stable Enterotoxin: Similar mechanism as the S. aureus enterotoxin and causes diarrhea with a much quicker onset of less than 8hrs
  • B. cereus spores can exist on grains such as rice and survive the cooking process. When left reheated for long periods the spores can germinate and grow, thus elaborating enterotoxins.
Clinical Consequences
  • Food Poisoning: Depending on which enterotoxin dominates the picture, infectious diarrhea may occur with different kinetics. If heat-labile enterotoxin dominates then diarrhea with onset 12-24hrs occurs which is generally watery. If heat-stable enterotoxin dominates then diarrhea with onset of less than 8hrs occurs together with nausea, vomiting, and abdominal pain.
  • Supportive therapy: Antibiotics are useless as the diarrhea is caused solely by ingestion of pre-formed enterotoxins.