Novel SCCmec type XII methicillin-resistant Staphylococcus aureus isolates identified from a swine production and processing chain

Methicillin-resistant Staphylococcus aureus (MRSA) has been a major public health concern. In this study, a total of 1485 samples from three swine farms, one slaughterhouse and one indoor market in Xiamen, China were collected in 2015, and the prevalence and profiles of MRSA were assessed. All the MRSA isolates were characterized by molecular typing, antibiotic susceptibility, coagulation activity, as well as PCR screening for 38 antibiotic resistance genes, two mobile genetic elements (lsa(E)-containing multiresistance gene cluster and Tn558), and 36 virulence genes. During the study, 54 of 1485 (3.6%) samples from the swine production, processing and retail chain were found positive for MRSA. A relatively rare SCCmecXII genotype was prevalent in swine farm (84.6%, 11/13) and slaughterhouse isolates (80.6%, 25/31), but absent in the market isolates (0%, 0/10). Notably, all staphylococcal cassette chromosome mec (SCCmec) type XII MRSA isolates were resistant to at least 6 classes of antibiotics, carried two mobile genetic elements (lsa(E)-containing multiresistance gene cluster and Tn558) and harbored multiple virulence genes. These multidrug resistant MRSA isolates could also coagulate both bovine and caprine plasma. Our results on the SCCmecXII MRSA isolates, particularly their profiles of related genotypes, antibiotic resistance and virulence determinants, illustrated the evolvement of livestock-associated (LA)-MRSA in the swine production environment and spread along the processing chain. The dominance of the SCCmecXII in MRSA isolates found in this study, differed from previous reports from China, indicated potential contribution associated with the production process.