Prevalence, Antibiotic Resistance, and Molecular Epidemiology of Staphylococcus aureus Isolated from Imported Foods in China

This 3-year surveillance study investigated the contamination patterns and genomic characteristics of Staphylococcus aureus in 2133 imported food samples, including frozen beef, frozen pork, frozen fish, frozen chicken, and cheese. An overall S. aureus contamination rate of 4.4% (93/2133) was observed, with frozen beef showing the highest prevalence (6.0%, 68/1139). The 93 isolates showed high resistance rates to ampicillin at 61.3% and penicillin at 58.1%. Methicillin-resistant S. aureus (MRSA) strains were identified in 14.0% (13/93) of them. Substantial genetic diversity was observed, with 24 sequence types (STs) and 41 spa types identified. The major prevalent clones included the globally prevalent ST5 (19.4%), of which 44.4% (8/18) carried at least one enterotoxin gene, as well as the livestock-associated ST398 (11.8%), which was significantly lower than its prevalence rate in China. The clone ST1460-t156 (10 strains) derived from equine-associated lineages was detected in strains isolated from beef samples. Virulence gene profiling revealed diverse enterotoxin carriage, with some strains carrying four or five enterotoxin genes simultaneously. Although a relatively low contamination rate of S. aureus was observed in the imported food products, the high prevalence of MRSA and carriage of several virulent strains necessitate close monitoring of S. aureus within global food supply chains to provide essential data for developing risk-based food safety interventions.