From soil to gut: Bacillus cereus and its food poisoning toxins.

Bacillus cereus is widespread in nature and frequently isolated from soil and growing plants, but it is also well adapted for growth in the intestinal tract of insects and mammals. From these habitats it is easily spread to foods, where it may cause an emetic or a diarrhoeal type of food-associated illness that is becoming increasingly important in the industrialized world. The emetic disease is a food intoxication caused by cereulide, a small ring-formed dodecadepsipeptide. Similar to the virulence determinants that distinguish Bacillus thuringiensis and Bacillus anthracis from B. cereus, the genetic determinants of cereulide are plasmid-borne. The diarrhoeal syndrome of B. cereus is an infection caused by vegetative cells, ingested as viable cells or spores, thought to produce protein enterotoxins in the small intestine. Three pore-forming cytotoxins have been associated with diarrhoeal disease: haemolysin BL (Hbl), nonhaemolytic enterotoxin (Nhe) and cytotoxin K. Hbl and Nhe are homologous three-component toxins, which appear to be related to the monooligomeric toxin cytolysin A found in Escherichia coli. This review will focus on the toxins associated with foodborne diseases frequently caused by B. cereus. The disease characteristics are described, and recent findings regarding the associated toxins are discussed, as well as the present knowledge on virulence regulation.

Food poisoning potential of Bacillus cereus strains from Norwegian dairies.

Characteristics concerning diarrhoeal potential were investigated in B. cereus dairy strains. The thirty-nine strains, isolated from whipping cream, were tested for cytotoxicity after culturing at human body temperature as well as 25 degrees C and 32 degrees C. At 37 degrees C, none of the strains were highly cytotoxic. This observation suggests that those strains should be considered to pose a minor risk with regard to diarrhoeal food poisoning. However, some strains were moderately or highly cytotoxic when grown at 25 degrees C and 32 degrees C. While the majority of the strains were able to grow at refrigeration temperatures, only four B. weihenstephanensis strains were identified among them when subjected to discriminative PCR assays and growth temperatures which delimit this species.