Analysis on the isolation, antimicrobial resistance and molecular epidemiological characteristics of MRSA of chicken origin in Hanzhong

ObjectiveTo clarify the prevalence， drug resistance， and epidemiological characteristics of methicillin-resistant Staphylococcus aureus （MRSA） isolated from chicken meat in Hanzhong， and provide useful insights for prevention of foodborne infections.MethodsA total of 196 retail chicken samples were collected from Hanzhong for isolation and identification of Staphylococcus aureus and MRSA. Antimicrobial susceptibility testing combined with whole-genome sequencing was used to analyze antimicrobial resistance characteristics， perform sequence typing （ST）， and identify toxin genes. The phylogenetic relationships among MRSA strains identified in this study were analyzed.ResultsThe MRSA detection rate was 18.9% （37/196）. More than 50% of these methicillin-resistant strains showed resistance to penicillin， erythromycin， clindamycin， tetracycline， and gentamicin. A total of four STs ［（ST9 （40.5%， 15/37）， ST59 （37.8%， 14/37）， ST398 （13.5%， 5/37）， and ST5 （8.1%， 3/37）］ were detected. ST9 and ST59 were the dominant clones identified in this study. The ST9 strain exhibited a higher prevalence of enterotoxin gene clusters than the ST59 strain， which carried fewer drug resistance genes but demonstrated a higher prevalence of the immune escape virulence genes sak and scn. Notably， the ST398 strain lacks enterotoxin genes， whereas the ST5 strain harbors the most diverse repertoire of virulence genes. In total， 23 virulence genes were identified. All strains carried the hemolysin genes hlgA， hlgB， hlgC， and the metalloproteinase gene aur. The prevalence of novel enterotoxins was higher than that of traditional enterotoxins. Genes encoding leukocidin and exoproteinases were also identified. The phylogenetic analysis reveals that strains sharing the same ST type are consistently grouped into a single clade within the evolutionary tree.ConclusionThe ST9 strain exhibited the highest isolation rate among chicken-associated MRSA in the Hanzhong region between 2019 and 2024， and was characterized by a high prevalence of enterotoxin gene clusters. During this period， the ST59 strain became the predominant clone in retail chickens in this region， with its notably high prevalence of immune escape genes.