Bacillus cereus emetic toxin production in cooked rice Original Research Article

Three mesophilic strains of Bacillus cereus known to produce emetic toxin were used to model germination, growth and emetic toxin production in boiled rice cultures at incubation temperatures ranging from 8°C to 30°C. Minimum temperatures for germination and growth in boiled rice were found to be 15°C for all strains. Toxin production at 15°C was found to be significantly greater (P<0·01; reciprocal toxin titre of 373±124) than at 20°C and 30°C (reciprocal toxin titres 112±37 and 123±41, respectively). Toxin production became detectable after 48 h incubation at 15°C, with a maximum titre reached by 96 h. At 20°C and 30°C, toxin production was detected at 24 h incubation, with a maximum titre reached by 72 h. Toxin production at 15°C was detectable at lower bacterial counts (6·2 log10 cfu g−1), than with incubation at 20°C and 30°C (>7·0 log10 cfu g−1). In this study, the lower temperature limit for germination and growth on solid laboratory medium was found to be 12°C for all strains, i.e. 3°C lower than that observed in boiled rice.