Isolation,Identification and Virulence Genes Investigation of Bacillus cereus from Ready-to-eat Products of Rice and Wheat

In order to investigate the contamination status and the distribution of virulence genes of Bacillus cereus from ready-to-eat products of rice and wheat,245 samples of ready-to-eat products of rice and wheat from catering service were selected for the pollution survey of B.cereus. Distribution of 13 virulence genes in 49 isolated B.cereus strains which were isolated by GB method and identified with housekeeping genes,were detected by PCR. The results showed that the average isolation rate of B. cereus in ready-to-eat products of rice and wheat was 10.61%(26/245). The detected positive samples were mainly bento and rice. Average detected quantity of B. cereus was 3032 CFU/g in this positive samples,in which bento were found to have the highest level. Two or more virulence genes in 49 isolated B. cereus strains were detected among which non-hemolytic enterotoxin genes nhe and entFM were the major virulence genes with the highest isolation rate,reaching 100% and 91.48%,respectively. The isolation rate of hemolysin genes hblA,hblC,hblD were 20.41%,38.78%,40.82%. There were 7(14.29%)strains with high virulent that carried 3 nhe genes and hblA,hblC,hblD virulence genes. And entFM gene was detected in the 7 high virulent strains. Emetic virulence genes(ces,cer,EM1)were detected only in 2 strains,with the isolation rate of 4.08%. The results gave guidance meaning for monitoring,early warning,tracing the infection source and transmission route after food poisoning,and it also could contribute to constructing the genetic fingerprinting library and molecular traceability platform of Bacillus cereus from ready-to-eat products of rice and wheat.