Bacillus cereus Toxins: Granum & Lund's 1997 Review

One Bacterium, Two Completely Different Food Poisonings

The study: Granum PE, Lund T. (1997). Bacillus cereus and its food poisoning toxins. FEMS Microbiology Letters, 157(2), 223–228.

Bacillus cereus is the overachiever of food poisoning — it causes two syndromes so different they look like unrelated diseases. There’s the diarrheal type (think C. perfringens-style, half a day later, from meats and sauces) and the emetic type — the infamous “fried rice syndrome,” vomiting within hours, looking for all the world like staphylococcal poisoning. Granum and Lund sorted out how one organism manages both tricks.

Two toxins, two stories

The diarrheal illness comes from enterotoxins produced in your intestine after you eat the bacteria. The emetic illness is the opposite: the toxin cereulide is preformed in the food — specifically in cooked rice left at room temperature — and it’s brutally heat-stable. Reheating doesn’t touch it. The timeline tells you which you’re dealing with: vomiting within hours means emetic; diarrhea after roughly half a day means diarrheal.

The spore problem

Here’s the part that catches people: B. cereus spores survive cooking. Normal boiling doesn’t kill them. So that pot of rice is sterile-ish when it comes off the heat, but the spores are sitting there waiting. Leave the rice at room temperature, and they germinate, multiply, and — in the emetic scenario — load the rice with toxin that no amount of stir-frying will remove.

The rice rule, with the science behind it

This paper is why every food safety code is obsessive about rice: cook it, cool it fast (spread it shallow, don’t leave it in the pot), refrigerate promptly, reheat once and thoroughly. Across the published studies, rice is the most commonly temperature-abused food in food service — it looks harmless sitting there, which is exactly the problem. When a vomiting outbreak follows fried rice service, don’t write it off as “stomach flu.” Think B. cereus emetic toxin, check the cooling logs, and you’ll usually find your answer.

The two syndromes, and why they demand different controls

Granum’s review clarified something that still confuses practitioners: B. cereus causes two distinct illnesses with different mechanisms, and they need different prevention. The emetic syndrome — the infamous fried-rice vomiting — comes from cereulide, a heat-stable toxin formed in the food before it’s eaten. Once it’s there, reheating won’t help; the rice was already a lost cause when it sat warm for hours. The diarrheal syndrome comes from enterotoxins produced in the gut after ingesting cells or spores — a different exposure, a longer incubation, a different control logic.

The emetic toxin’s heat stability is the point most operations underappreciate. Standard cooking and reheating destroy the vegetative cells effortlessly, which creates false confidence — the food tests clean-ish, smells fine, and still carries a toxin that survives boiling. Control has to be about preventing formation: rapid cooling of cooked rice and pasta, limited holding times, and refrigeration that actually reaches temperature quickly. The spore survival through cooking is expected; the failure is everything that happens after.

For cook-chill and cook-serve operations, B. cereus is the organism that validates your cooling logs. Every rice, pasta, or grain dish sitting in the danger zone is a cereulide production opportunity, and the spores are guaranteed present — they’re in the raw ingredient. The review’s lasting practical message: you cannot cook your way out of poor cooling. The kill step handles the cells; only time-temperature discipline handles the toxin.

Source: Granum PE, Lund T. (1997). Bacillus cereus and its food poisoning toxins. FEMS Microbiology Letters, 157(2), 223–228.