Genetic Diversity, Virulence Profiles, and Antimicrobial Resistance of Bacillus cereus Group Isolates from Foods in Eastern China.

Bacillus cereus group strains are common foodborne pathogens that can cause vomiting, diarrhea, and other diseases. Here, we isolated 35 strains of B. cereus from the food in school cafeterias. Whole-genome sequencing (WGS) identified that the isolates belonged to B. cereus sensu stricto and B. mosaicus (panC Group III/IV). Based on the multilocus sequence typing (MLST) scheme, 16 sequence types (STs) were identified, including the emetic clone ST26 and a new sequence type ST3408. The dominant clonal complex was 142. Phylogenetic analysis based on single-nucleotide polymorphism (SNP) analysis revealed significant genetic variations, with the ST26 clade being independent of other clades. Virulence gene analysis revealed that diarrheal toxin genes were common: nhe (100%), hbl (71.4%), and cytK (80.0%). The emetic toxin gene ces appeared in three isolates (8.6%). Antimicrobial resistance genes were common. Each isolate carried intrinsic β-lactamase genes, as well as the fosB gene. In addition, genes conferring resistance to tetracyclines, macrolides, and streptomycin were detected in 25.7%, 20.0%, and 82.9% of the isolates, respectively. The resistance to β-lactam antibiotics was confirmed with phenotypic antimicrobial susceptibility testing. The antimicrobial phenotypes of some strains were inconsistent with their carriage of antimicrobial resistance genes. These results indicate that the genetic diversity and antimicrobial resistance exhibited by B. cereus from the food sources in the cafeterias may pose a potential hazard to student food safety.