Detection and differentiation of non-emetic and emetic Bacillus cereus strains in food by real-time PCR

Duplex real-time polymerase chain reaction (PCR) method was developed for direct detection and identification of non-emetic and emetic Bacillus cereus strains in foods without enrichment. Primers and TaqMan probes were designed for molecular chaperonin gene groEL and cereulide synthetase gene ces. A total of 62 B. cereus strains, of which 59 were non-emetic and 3 emetic, were found positive by groEL-specific conventional PCR. Three emetic strains were found by cesspecific PCR to be positive, whereas 59 non-emetic strains were negative. Ten strains other than B. cereus were all negative by both groEL-specific and ces-specific PCR assays. The limits of detection of the duplex PCR assays for both non-emetic and emetic strains from their pure cultures were 3× 100 CFU/reaction. A total of 10 doenjang (traditional Korean fermented soybean paste) samples were analyzed simultaneously by real-time PCR assay and analytical profile index (API) test kits. All tested samples were positive for B. cereus contamination except two samples. The result of the real-time PCR assay was consistent with that of the API test. Among the eight positive samples, six and two samples were contaminated with non-emetic and emetic strains, respectively. The results suggest that the real-time PCR method developed in the present study may be useful for the direct detection and differentiation of B. cereus strains in foods.