Prevalence of methicillin-resistant Staphylococcus aureus in Canadian commercial pork processing plants

Aims: This study investigated the prevalence of Methicillin-resistant Staphylococcus aureus (MRSA), their spa-types, and antimicrobial resistance profiles at various steps during commercial pork production from three plants designated as A, B and C. Methods and Results: Over a period of 1 year 2640 samples from three commercial pork plants were obtained on a rotating basis. Sample sources were: nasal swabs after bleeding (NSAB), nasal swab after scalding (NSASs, plant C) or skinning (NSASk, plants A, B), carcass swabs after pasteurization (CSAP, plant C) or washing (CSAW, plants A, B) and retail pork (RP). Overall MRSA prevalence at each sampling point in the pork plants after adjusting for clustering was: 61·93, 28·38 7·58 and 1·21% for NSAB, NSASc/Sk, CSAP/CSAW and RP respectively. The majority of MRSA isolates from the three pork plants belonged to livestock-associated MRSA spa-types t034 and t011 (3·8%; ST398). The mainly human spa-type t002 (15%) was also recovered. All MRSA isolates were resistant to β-lactam and tetracycline antibiotics. Overall resistance to tigecycline was found in about 10% of MRSA isolates while <3% isolates were resistant to daptomycin, gentamicin, quinupristin/dalfopristin and trimethoprim/sulfamethoxazole. Conclusion: A higher prevalence of MRSA in the nasal cavity of incoming pigs was observed at all three plants, but a notable reduction in MRSA along the pork processing steps occurred. Significance and Impact of the Study: The highest prevalence of MRSA was found in the nasal cavity of incoming pigs in three commercial pig slaughter and pork processing plants. A reduction in MRSA prevalence occurred along the processing chain, and pork products from these plants showed significantly lower MRSA than the initial steps of slaughter and processing, suggesting a reduction in MRSA during the slaughter process with minimal cross-contamination.