Diarrhoeal toxin production at low temperature by selected strains of Bacillus cereus

The growth of four Bacillus cereus strains producing diarrhoeal toxin at 32 degrees C (F4433/73 and 29.155, isolated on the occasion of foodborne outbreaks, and F4581/76L and F4581/76R, two variants of a clinical strain), a weakly toxigenic strain isolated in routine analysis of food (3505M) and an emetic isolate (F3502/73) was investigated at low temperature. Biomass was determined by protein assay. Generation times were: for strain F3502/73, which grew at greater than or equal to 12 degrees C, 8.71 h (at 12 degrees C); for other strains, which grew at greater than or equal to 10 degrees C, 10.2 to similar to 18.9 h (at 10 degrees C). Toxin production during growth was evaluated by a commercial kit (Oxoid) and by a toxicity test on Chinese hamster ovary cells. Strains F4433/73 and F4581/76, secreting high levels of diarrhoeal toxin during the exponential phase at 32 degrees C, produced high levels of toxicity at 10 degrees C until the stationary phase. Strain 29.155 had decreased toxin production at 10 degrees C. Toxicities for cellular extracts remained low when compared with culture filtrates. A correlation was found between the toxicity values given by the two detection methods tested, and the suitability of both methods for the detection of potential poisoning isolates is discussed.