Genomic characterization of isolated from food poisoning cases revealed the mechanism of toxin production.

INTRODUCTION

is a ubiquitous opportunistic human pathogen that causes food intoxications worldwide. However, the genomic characteristics and pathogenic mechanisms of are still unclear.

METHODS

Here, we isolated and purified nine strains of () that caused vomiting, diarrhea and other symptoms from four foodborne outbreaks happened in Guizhou Province in southwest China from June to September 2021. After colony observation, Gram staining, microscopic examination and biochemical test, they were identified as . The genomic characteristics, phylogenetic relationships and virulence factors of the isolated strains were analyzed at the genome level. Genome sequencing, comparative genomic analysis, secondary metabolite analysis and quantitative PCR were utilized to give a thorough exploration of the strains.

RESULTS

We obtained the genome maps of and found that had a complex interspecific relationship with B. anthracis and . We also observed a contraction of gene families in , and the contracted families were mainly associated with prophage, which contributed to the species diversity of . The gene family underwent a rapid evolution in , which facilitated the adaptation of the strains to adverse environmental conditions. Moreover, the strains exhibited a higher copy number in the non-ribosomal polypeptide synthetase (NRPS) genes and carried the complete cereulide synthetase () gene cluster sequences. Considering that the system is a classical regulatory mechanism for emetic toxin synthesis, we hypothesized that could synthesize emetic toxins through the regulation of gene clusters by the system.

DISCUSSION

These findings are important for further investigation into the evolutionary relationship between and their related species, as well as the underlying mechanisms governing the synthesis and secretion of bacterial toxins.