Diversity and toxigenicity among members of the Bacillus cereus group

Members of the Bacillus cereus group were isolated from rice products by centrifugation-plating and conventional spread-plating methods. Random amplified polymorphic DNA-polymerase chain reaction (RAPD-PCR) results showed broad diversity among the strains and revealed some associations among isolates from raw and cooked rice samples, at the genotypic level. A comparatively greater diversity among strains was observed in isolates from raw rice than those from cooked rice and, generally, the RAPD profiles of isolates from raw and cooked rice were different, with only a few of them common to both types of rice. The toxigenic potential of the isolates was also determined by molecular and immunoassay analyses. The results revealed that most isolates from the B. cereus group were potentially or actually toxigenic, and some isolates could produce both diarrhoeal and emetic toxins. Generally, isolates belonging to the B. cereus group with the same RAPD pattern were shown to have a similar profile of enterotoxigenicity.

► Bacillus cereus group isolated from Australian rice products was analysed.
► RAPD-PCR showed greater genetic diversity in raw than in cooked rice isolates.
► Most isolates from the B. cereus group were potentially or actually toxigenic.
► Some isolates could produce both diarrhoeal and emetic toxins.
► Isolates with the same RAPD pattern had a similar enterotoxigenicity profile.