Bacillus cereus

Bacillus cereus is a gram-positive bacterium widespread in the environment, especially in soil and dust. It produces two types of toxins, one stable to heat, which causes vomiting, another, labile to heat, responsible for a diarrheal form in unsuitable environmental conditions. Bacillus cereus is a sporigenous bacterium, that is, when environmental conditions are adverse, it is able to switch from its canonical “vegetative” form to the “spore” state, a form of resistance that guarantees its survival. a form of resistance that guarantees its survival for long periods.

The Bacillus cereus group includes eight species, one of which, Bacillus thuringiensis, is used as a biopesticide against insects. According to EFSA (the European Food Safety Agency) experts, the only way to correctly identify Bacillus cereus group strains is to map their entire genome sequence.

Bacillus cereus and Bacillus thuringiensis strains are usually not discriminated in clinical diagnostics or food microbiology, although to date there is no evidence that Bacillus thuringiensis possesses the genetic determinants for the production of the emetic toxin.

Contamination

The infection can occur through contaminated food. In particular, those foods that are kept at room temperature for a long time after cooking or that have not been rapidly and effectively cooled are associated with cases of toxinfection. This is because Bacillus cereus is able to survive in a spore state during the heat treatment of the food and then mutate into the vegetative form (capable of producing toxins) when conditions become favorable again for its survival.

The most frequently contaminated food types are :

  • rice-based foods, which are the most important source of disease for humans, and foods with starch (e.g. potatoes, pasta) (especially for the emetic form);
  • mixed products such as sauces, soups, puddings, casseroles, meat and milk preparations;
  • properly cooked unprocessed foods such as meat, milk, vegetables and fish (most frequently associated with the diarrheal form);
  • pastry products;
  • salads and other vegetables;
  • tofu.

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