Characterisation of meticillin-resistant Staphylococcus aureus ST97 and ST5 isolated from pigs in Japan

The objective of this study was to determine the frequency and clonal types of meticillin-resistant Staphylococcus aureus (MRSA) among slaughter pigs in a top pig-producing area in Japan. In total, 100 nasal swabs were collected from slaughterhouse pigs originating from 21 different farms. MRSA isolates were analysed by staphylococcal cassette chromosome mec (SCCmec) typing, spa typing and multilocus sequence typing (MLST) and were examined for susceptibility to nine antimicrobial agents (ampicillin, oxacillin, gentamicin, kanamycin, erythromycin, clindamycin, vancomycin, ciprofloxacin and tetracycline). MRSA isolates were obtained from eight swabs (8%), representing three pig farms (14%). Five of the isolates were classified as ST97/spa t1236/SCCmec V and three were classified as ST5/spa t002/atypical SCCmec type. All of the isolates were resistant to ampicillin, oxacillin and tetracycline, and seven isolates (88%) were resistant to clindamycin. The five ST97 MRSA isolates displayed an unusual phenotype (clindamycin-resistant/erythromycin-susceptible). In conclusion, this is the first report of a ST97 MRSA isolate in Japan. The overall prevalence of MRSA is low in pigs, although it appears to be adapting among pigs in Japan owing to the new ST97 and ST5 MRSA strains.