Detection of Bacillus cereus in foods by colony hybridization using PCR-generated probe and characterization of isolates for toxins by PCR

Isolates of Bacillus cereus from traditional Indian foods were detected by colony hybridization using the PCR-generated phospholipase (PL-1) probe. In all, 29 isolates picked up by the probe were confirmed as B. cereus by conventional cultural and biochemical characteristics. All the isolates reacted positively in PCR with phospholipase (PL-1) primers. Among the native isolates, 11 of them showed the discontinuous pattern of haemolysin BL activity in gel diffusion assay. Though 14 isolates reacted positively in PCR with primers (Ha-1) specific to the B gene of haemolysin BL, only four of them showed both the presence of gene and haemolysin BL activity. More than 50% of the isolates indicated their potential enterotoxigenicity by reacting positively with primers specific for the BceT gene encoding for diarrhoeal enterotoxin. PCR with primers for different inverse (IS) repeat elements revealed that isolates carrying transposon IS 231–P 231-1 did not carry IS 240–P 240. Some of the isolates were devoid of these IS elements. The study demonstrated the potential of using of a PCR-generated labelled PL-1 probe for the direct detection of B. cereus in food samples and PCR for characterizing the toxigenic isolates.