Analysis of genomic characteristics and virulence factors of emetic-type Bacillus cereus strains isolated in Hangzhou

Objective To investigate the genomic characteristics and virulence factors of emetic-type Bacillus cereus strains isolated from food in Hangzhou for better understanding their pathogenic potential. Methods Real-time PCR was performed to detect the ces gene cluster (cereulide) in 132 Bacillus cereus strains isolated from food from 2015 to 2017. Genomes of cereulide-positive strains were sequenced using Illumina MiSeq sequencing platform. Genome annotation, virulence factor detection, comparative and evolutionary analysis were performed after the sequences of genomes were assembled. Results Twelve strains (9.09%) carried the ces gene. Their genome sizes ranged from 5.35 to 5.75 Mb and GC contents from 35.25 to 35.43 mol%. All of them harbored the full cereulide biosynthesis gene cluster, nonhemolytic enterotoxin (NHE)-encoding gene cluster (nheA, nheB and nheC) and hemolysin Ⅲ (hlyⅢ). The average nucleotide identity (ANI) between the 12 isolates and the reference strain NC7401 (Accession number: AP007209) was over 99.35%. Phylogenetic analysis demonstrated these strains were clustered into the same branch with local clinical isolates and the emetic-type Bacillus cereus strains of NC7401 and AH187. Conclusions The genomic sequences of the emetic-type Bacillus cereus strains isolated from food in Hangzhou area were highly similar to that of the reference strain NC7401. Results of the genomic analysis suggested that these isolates carried many virulence factors that were related to pathogenicity. Key words: Bacillus cereus; Genome sequencing; Virulence factor; Genomic analysis