Atlas of foodborne infections
transmitted by contaminated food and water

Atlas of Patogens Contents Information sources Glossary Administration

Bacillus cereus

CZ: Bacillus cereus
EN: Bacillus cereus

Occurrence:
Meat and Meat Products
Milk and Milk Products
Soft Cheeses
Hard Cheeses
Fish and Fish Products
Fruits and Vegetables
Cereals


Category:
Bacteria


Foodborne Disease:
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B. cereus causes two types of food-borne illnesses:


Description:
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The short-incubation form is caused by a preformed, heat-stable emetic toxin, ETE. The mechanism and site of action of this toxin are unknown, although the small molecule forms ion channels and holes in membranes.

The long-incubation form of illness is mediated by the heat-labile diarrheagenic enterotoxin Nhe and/or hemolytic enterotoxin HBL, which cause intestinal fluid secretion, probably by several mechanisms, including pore formation and activation of adenylate cyclase enzymes.

TOXINS

Bacillus cereus produces one emetic toxin (ETE) and three different enterotoxins: HBL, Nhe,and EntK.
Two of the three enterotoxins are involved in food poisoning. They both consist of three different protein subunits that act together. One of these enterotoxins (HBL) is also a hemolysin; the second enterotoxin (Nhe) is not a hemolysin. The third enterotoxin (EntK) is a single component protein that has not been shown to be involved in food poisoning. All three enterotoxins are cytotoxic and cell membrane active toxins that will make holes or channels in membranes. B. cereus food poisoning occurs year-round and is without any particular geographic distribution. 

The short-incubation form is most often associated with rice dishes that have been cooked and then held at warm temperatures for several hours. It is often associated with Mexican and Chinese restaurants, but in one reported outbreak, macaroni and cheese made from powdered milk turned out to be the source of the bacterium. “Mac and cheese”- you can’t get much more  American than that. Disease is diagnosed by the isolation of B. cereus from the incriminated food.

Long-incubation B. cereus food poisoning is frequently associated with meat or vegetable-containing foods after cooking. The bacterium has been isolated from 50% of dried beans and cereals and from 25% of dried foods such as spices, seasoning mixes and potatoes. One outbreak of the long-incubation form was traced to a “meals-on-wheels” program in which food was held above room temperature for a prolonged period before delivery to consumers. Disease is diagnosed by isolation of the organism from stool and food. Isolation from stools alone is not sufficient because 14% of healthy adults have been reported to have transient gastrointestinal colonization with B. cereus.

Because B. cereus gastroenteritis is generally a benign, self-limited illness, antimicrobial agents are of no value in management. Since the bacteria grow best at temperatures ranging from 40 to 140°F, infection may be prevented if cold food is refrigerated and if hot food is held at greater than 140°F before serving. 


Pictures:

Bacillus cereus
Source: Bacillus cereus colonies on blood agar
Bacillus cereus
Source: Detail of Bacillus cereus colonies on blood agar
Bacillus cereus
Source: Patogens under the light microscope (colored)
Bacillus cereus
Source: Patogens under the scan microscope (colored)

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