Epidemiological typing of Bacillus spp. isolated from food.

Biotypes, fatty acid profiles, and restriction fragment length polymorphisms of a PCR product (PCR-RFLP of the cereolysin AB gene) were compared for 62 isolates of the Bacillus cereus group. Eleven isolates originated from various foods, and 51 isolates were obtained from pasteurized milk which had been processed by two different dairies. The isolates were clustered into 6 biotypes, 10 fatty acid groups, or 7 PCR-RFLP clusters. Isolates with mesophilic or psychrotrophic characteristics were preferentially distributed into specific fatty acid or PCR-RFLP groups (P = 0.004). Unique fatty acid clusters were predominantly found in milk samples of each dairy (P < 0.0001), suggesting that certain dairy plants may harbor plant-specific B. cereus which might constantly contribute to postpasteurization contamination.