Bacillus cereus Gastroenteritis

Bacillus cereus is an aerobic, spore-forming rod normally present in soil, dust, and water. It has been associated with food poisoning in Europe since at least 1906. Among the first to report this syndrome with precision was Plazikowski. His findings were confirmed by several other European workers in the early 1950s.

Low numbers of this bacterial species can be found in a number of food products, including fresh and processed foods. In a study of raw meats, meat products, and product additives, B. cereus was found in 6.6% of 534, 18.3% of 820, and 39.1% of 609 samples, respectively,61 with levels of 102– 104/g. It is unclear if any were enterotoxigenic. Enterotoxigenic strains were recovered from a variety of foods in another study, with 85% of 83 strains from raw milk being positive for the diarrheagenic toxin.

In addition to B. cereus, B. mycoides strains from milk have been shown to produce diarrheagenic enterotoxin in nine days at temperatures between 6◦C and 21◦C. Varying numbers of isolates of the following species were found also to be enterotoxin producers: P. circulans, B. lentus, B. thuringiensis, B. pumilus, P. polymyxa, B. carotarum, and B. pasterurii.43 B. thuringiensis has been isolated from foods, and it apparently produces a Vero-cell active toxin.

This bacterium has a minimum growth temperature around 4–5◦C, with a maximum around 48–50◦C. Growth has been demonstrated over the pH range 4.9–9.3.40 Its spores possess a resistance to heat typical of other mesophiles.

B. cereus Toxins

This bacterium produces a wide variety of extracellular toxins and enzymes, including lecithinase, proteases, β-lactamase, sphingomyelinase, cereolysin (mouse lethal toxin, hemolysin I), and hemolysin BL. Cereolysin is a thiol-activated toxin analogous to perfringolysin O. It has a molecular weight of 55 kDa and apparently plays no role in the foodborne gastroenteritis syndromes.

 

Diarrheal Syndrome

This syndrome is rather mild, with symptoms developing within 8–16 hours, more commonly within 12–13 hours, and lasting for 6–12 hours.

Symptoms consist of nausea (with vomiting being rare), cramplike abdominal pains, tenesmus, and watery stools. Fever is generally absent. The similarity between this syndrome and that of C. perfringens food poisoning has been noted.

Emetic Syndrome

This form of B. cereus food poisoning is more severe and acute than the diarrheal syndrome. The incubation period ranges from 1 to 6 hours, with 2 to 5 hours being most common. Its similarity to the staphylococcal food-poisoning syndrome has been noted.34 It is often associated with fried or boiled rice dishes. In addition to these, pasteurized cream, spaghetti, mashed potatoes, and vegetable sprouts have been incriminated.

The emetic (vomiting type) toxin has been determined to be cereulide, an ionophoric,water-insoluble peptide that is closely related to the peptide antibiotic valinomycin. The strains produced 80 to 166 μg of cereulide/ml at 21◦C in 1 to 3 days during the stationary growth phase when cell numbers reached 2 × 108 to 6 × 108 cfu/ml. Production at 40 and below 8◦C was minimal.

The emetic toxin strains grow over the range 15–50◦C, with an optimum between 35◦C and 40◦C. Whereas the emetic syndrome is most often associated with rice dishes, growth of the emetic toxin strains in rice is not favored in general over other B. cereus strains, although higher populations and more extensive germination have been noted in this product.

Reviewed from: Modern Food Microbiology 7th Edition. Food Science Text Series.