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Bacillus cereus, a commonly occurring pathogen which can survive in remarkably hostile conditions, is typically found in soil. Illness associated with B. cereus can occur when heat-resistant B. cereus endospores survive cooking. If the food is then inadequately refrigerated or held for extended periods at improper temperatures the endospores can germinate and multiply. Once the spores germinate, the vegetative cells can multiply and produce illness causing enterotoxins. B. cereus is known to cause two distinctly different types of food-borne illness.
- The first type of illness, referred to as the Rapid-onset (Emetic) Vomiting-type, is characterized by nausea and vomiting. The incubation period ranges from 1 to 6 hours. Both the symptomology and incubation period mirror those of Staphylococcus aureus.
- The second type of illness, generally referred to as the Slow-onset Diarrheal-type, is characterized by diarrhea and abdominal pain. The diarrheal-type illness has an incubation period ranging from 6 to 24 hours. The symptoms include watery diarrhea, abdominal cramps and pain. This type generally mimics the symptoms of Clostridium perfringens.
Regardless of type, symptoms typically persist for less than 24 hours. Generally, gastroenteritis symptoms from B. cereus resolve by themselves. In very rare cases, however, some degree of medical intervention may be required.
The diarrheal-type food poisoning has been associated with a wide variety of foods, including meat and vegetable dishes, sauces, pastas, desserts and dairy products. In turn, the vomiting-type outbreaks have typically been associated with rice products. Other starchy foods such as potato, pasta and cheese have also been implicated. Some outbreaks may ultimately go unreported because of the similarities between B. cereus, Staphylococcus aureus intoxication (B. cereus vomiting-type) and C. perfringens food poisoning (B. cereus diarrheal-type).
B. cereus and B. anthracis may pose a higher risk to those working in food preparation areas and slaughterhouses. While intact tissues and meat from animals are sterile, once slaughtered, the potential for contamination emerges.
The presence of large numbers of B. cereus (greater than 10^6 organisms /g) in a food can be indicative of active growth and proliferation of the organism. Confirmation of B. cereus as the etiologic agent in a food-borne illness outbreak requires, at the very least: (1) isolation of strains of the same serotype from the suspect food and patient; (2) isolation of large numbers of a B. cereus serotype known to cause food-borne illness from the suspect food and patient, and (3) isolation of B. cereus from suspect foods and determining their enterotoxigenicity by serological (diarrheal toxin) or biological (diarrheal and emetic) tests. According to the FDA, the rapid onset time from consumption to symptoms in the emetic form of the disease, coupled with microbiological evidence, is often sufficient to diagnose this type of food poisoning.
Schneider et al., "Preventing Foodborne Illness: Bacillus cereus and Bacillus anthracis ". Florida Cooperative Extension Service, University of Florida. November, 2004.