Study of the drug sensitivity, virulence genes and molecular typing of Bacillus cereus in five foods in Haikou

Objective To study the distribution, virulence genes, drug sensitivity and molecular characteristic of Bacillus cereus in five foods in Haikou area. Methods The Bacillus cereus strains were isolated from different foods including pastries, milk powder, fast food, Hainan rice noodles and its ingredients, collected from Haikou area, according to the standard GB 4789.14-2014. The specific gene groEL and 10 virulence genes were detected by general polymerase chain reaction (PCR) method. The sensitivity to antibiotics of isolates was performed with minimum inhibitory concentration (MIC). The pulsed field gel electrophoresis (PFGE) patterns of strains were analyzed. Results 197 strains of B. cereus were isolated from 626 food samples and the positive rate of B. cereus was 31.5%. In particular, most of B. cereus strains were isolated from Hainan rice noodles, accounting for 63.1% (140/222). All isolates carried at least one virulence gene, the rate of entFMgene was the highest, up to 99.0% (195/197). On the contrary, ces gene was the lowest at 2.5% (5/197) only. There were 175 (88.8%) strains that carried genes of nheA, nheB and nheC simultaneously. There were 27 (13.7%) strains that carried genes of hblA, hblC and hblD simultaneously. The sensitive rate of strains towards gentamicin, chloramphenicol, vancomycin and ciprofloxacin were 100.0% (197/197), 100.0% (197/197), 99.5% (196/197) and 92.9% (183/197), respectively. And the resistance rate of strains towards penicillin and trimethoprim-sulfamethoxazole were 100.0% (197/197) and 90.9% (179/197), respectively. The PFGE result showed 30 clusters and 117 genotypes. Conclusion The positive rate of Bacillus cereus in five foods in Haikou area was relatively high, especially in Hainan rice noodles, which should arouse attention and close observation. Targeted prevention and control measures can be carried out according to the characteristics of virulence genes, molecular typing and antibiotic sensitivity of the strains