To assess the cross-contamination risk and genetic evolution ofStaphylococcus aureus(S.aureus)at various stages in a swine slaughterhouse,and to provide a reference for risk evalua-tion and control measures of S.aureus contamination during swine slaughtering,we conducted whole-genome sequencing on 31 isolates of S.aureus collected and preserved from the slaughter-house.Bioinformatics analyses were performed to investigate the genomic characteristics and genet-ic relationships of these isolates.Results revealed cross-contamination across different slaughter-house stages,predominantly with ST398-t1451 strains.Additionally,highly virulent ST9-t899 strains and ST398-t11 strains with numerous resistance genes were detected at various stages.The strains predominantly carried virulence genes such as hlgA,hlgB,and hlgC,with varying num-bers of resistance genes.Notably,two strains carried the optrA gene and three strains carried the cfr gene;the presence of the optrA gene is relatively rare among S.aureus.These genes confer re-sistance to novel synthetic antibiotics such as oxazolidinones and florfenicol and have the potential for horizontal gene transfer,increasing the risk of dissemination both within and beyond the slaughterhouse.Importantly,the study also detected a LA-MRSA-ST9 strain in water samples from the slaughterhouse,which could potentially infect humans.This strain exhibits zoonotic char-acteristics,highlighting the need for stricter protective measures for slaughterhouse workers to mitigate occupational exposure and infection risks.

To assess the cross-contamination risk and genetic evolution ofStaphylococcus aureus(S.aureus)at various stages in a swine slaughterhouse,and to provide a reference for risk evalua-tion and control measures of S.aureus contamination during swine slaughtering,we conducted whole-genome sequencing on 31 isolates of S.aureus collected and preserved from the slaughter-house.Bioinformatics analyses were performed to investigate the genomic characteristics and genet-ic relationships of these isolates.Results revealed cross-contamination across different slaughter-house stages,predominantly with ST398-t1451 strains.Additionally,highly virulent ST9-t899 strains and ST398-t11 strains with numerous resistance genes were detected at various stages.The strains predominantly carried virulence genes such as hlgA,hlgB,and hlgC,with varying num-bers of resistance genes.Notably,two strains carried the optrA gene and three strains carried the cfr gene;the presence of the optrA gene is relatively rare among S.aureus.These genes confer re-sistance to novel synthetic antibiotics such as oxazolidinones and florfenicol and have the potential for horizontal gene transfer,increasing the risk of dissemination both within and beyond the slaughterhouse.Importantly,the study also detected a LA-MRSA-ST9 strain in water samples from the slaughterhouse,which could potentially infect humans.This strain exhibits zoonotic char-acteristics,highlighting the need for stricter protective measures for slaughterhouse workers to mitigate occupational exposure and infection risks.