Bacillus cereus is the bacterial equivalent of a bipolar personality. Depending on the strain, it can cause either of two syndromes – a rapid onset emetic syndrome, or a slower onset intestinal upset.

Some history

The first reported description of Bacillus cereus food poisoning was published in 1950. The earliest documented US outbreak occurred in 1969. Two years later, the United Kingdom confirmed its first outbreak of Bacillus cereus food poisoning.

What is Bacillus cereus, and where is its natural habitat?

Bacillus cereus is a spore-forming soil microbe. It is widely distributed around the world, but has no known animal reservoir. The microbe is able to grow either in the presence or in the absence of oxygen. Its spores are sufficiently heat-resistant to survive pasteurization treatment of milk and standard cooking temperatures reached in domestic kitchens. It cannot survive the high-temperature treatment used to process canned foods.

How is Bacillus cereus transmitted? What is the incubation period of the illness?

Bacillus cereus strains produce one of two toxins – a heat-stable emetic toxin that is produced in the food as the microbe grows, and a heat-sensitive enterotoxin that is produced both in the food and in the intestines. Ingestion of the emetic toxin triggers the onset of nausea and vomiting, which can begin as soon as 30 minutes after a victim eats food containing the preformed toxin. Ingestion of the heat-sensitive enterotoxin (or its production in the intestines) results in the development of a diarrhetic syndrome that can begin some 8 to 16 hours after the toxin enters the body.

What are the symptoms of Bacillus cereus food poisoning?

Emetic syndrome:- In most individuals, the preformed heat-stable emetic toxin of Bacillus cereus triggers a bout of nausea and vomiting that can being from 30 minutes to 5 hours after eating a contaminated dish and typically lasts for 6 to 24 hours. This form of food poisoning can be confused with Staphylococcus aureus food poisoning.

Diarrhetic syndrome:- The onset of this form of Bacillus cereus food poisoning is slower than for the emetic syndrome – approximately 8 to 16 hours. The main symptoms are a profuse, watery diarrhea and abdominal pain, usually lasting about 12 to 24 hours. This food poisoning syndrome mimics the symptoms produced by Clostridium perfringens enterotoxin.

What is the prognosis of Bacillus cereus food poisoning?

Both forms of Bacillus cereus food poisoning are typically mild and self-limiting. Individuals who are already suffering from a debilitating illness or someone with a compromised immune system may suffer from dehydration. Someone whose swallowing reflex is impaired could accidentally aspirate vomit, resulting in lung complications.

What foods carry Bacillus cereus?

As a common soil inhabitant, Bacillus cereus is most likely to be found on harvested crops – grains, fruits and vegetables. Because the spores are heat-resistant and survive normal cooking conditions, Bacillus cereus food poisoning is most commonly associated with consuming cooked, starchy foods – such as rice dishes – that have been held at room temperature for several hours after cooking.

How can people protect themselves from Bacillus cereus?

First, by paying attention to food recall announcements and immediately discarding any recalled food or returning it to the store. Secondly, by not allowing a cooked food to stand for extended periods of time at room temperature. Food that is not to be eaten immediately should be refrigerated or frozen promptly. A frozen, cooked food should be thawed in the refrigerator, and not at room temperature.

For more information on Bacillus cereus and other food-borne pathogens, visit the CDC website or read Food Safety: Old Habits, New Perspectives.