Genomic and virulence characteristics of Staphylococcus aureus isolates from foodborne outbreak cases

This study aimed to investigate the genomic characteristics, enterotoxin production, and antimicrobial resistance profiles of Staphylococcus aureus isolates associated with foodborne outbreaks. A total of 19 bacterial isolates were collected from foodborne outbreaks in Guizhou Province, China between 2014 and 2023. Following biochemical identification, all isolates were confirmed as S. aureus. Phylogenetic analysis divided the 19 strains into seven branches. Enterotoxin production was detected using standard microbiological techniques and immunoassays. Antimicrobial susceptibility was evaluated using the broth microdilution method. Whole-genome sequencing and subsequent bioinformatic analyses were conducted to characterize virulence genes, antimicrobial resistance genes, multilocus sequence typing (MLST) genotypes, and phylogenetic relationships among the isolates. This study found that all strains produced classical staphylococcal enterotoxins, with staphylococcal enterotoxin (SEA) showing the highest detection rate (63.16%). Virulence gene profiling revealed widespread presence of hlb, hlgA, nuc, clfB, spa, and set genes. All strains were resistant to penicillin, with high resistance rates for erythromycin and cefoxitin. Multidrug resistance occurred in 11 of the 19 strains, and 22 resistance genes were identified. MLST analysis showed that ST6 and ST59 were the dominant types, with ST59 methicillin-resistant S. aureus (MRSA) strains displaying stronger resistance and more virulence determinants. These findings provide insights into the virulence, resistance, and molecular epidemiology of S. aureus strains involved in foodborne outbreaks, and may provide useful information for future surveillance and risk assessment.