Virulence gene detection and antimicrobial susceptibility analysis of Bacillus cereus fresh food isolates

Objective:To isolate and identify Bacillus cereus in food and further investigate the virulence genes and antimicrobial resistance of Bacillus cereus fresh food isolates.Methods:100 fresh food products samples were collected from food markets and food stands of Chengdu,respectively.Then,Bacillus cereus strains were identified by MYP selective medium. 16S rRNA sequencing analysis was used to further identify Bacillus cereus species. Virulence genes of Bacillus cereus were detected by PCR method. The susceptibility of Bacillus cereus to 18 antibiotics was detected by disk diffusion method. Results:24 strains of Bacillus cereus fresh food isolates were detected from 100 fresh food samples,the isolation rate was 24%.The detection rates of Bacillus cereus from food stands samples were 70%,much higher than that from food markets samples(18.9%). Among all the 13 virulence genes,both ces and cer were only found to be occurred in one isolate,with a very low detection rate,nheC occurred in 24 isolates,cytK occurred in 13 isolates,bceT occurred in 12 isolates,hblA occurred in 11 isolates,nheB occurred in 10 isolates,hblC,nheA and hblD occurred in 9 isolates,hly-Ⅱ occurred in 7 isolates,hblB and entFM were not found,the detection rates for4 housekeeping genes(rpoB,gyrB,groEL and vrrA)were100%. Bacillus cereus fresh food isolates showed high resistance to bacitracin B,sulfamethoxazole,oxacillin and penicillin,and the resistant rate was more than 96%. For amikacin,chloramphenicol,gentamicin,and amphenol,the resistance rates were less than 7%. Conclusion:The results would lay a foundation for further assessing the risk of Bacillus cereus in fresh food.