Identification of a mecA/mecC-positive MRSA ST1-t127 isolate from a racehorse in Japan

Objectives MRSA is a known pathogen that affects horses. We investigated an equine MRSA isolate for potential antimicrobial resistance genes, classified the staphylococcal cassette chromosome mec (SCCmec) and identified the strain-specific dissemination in the horse community based on WGS. Methods WGS, using short-read sequencing, and subsequent long-read sequencing by hybrid assembly, was conducted to obtain a complete genome sequence. Pairwise sequence alignment of relative SCCmec sequences and core-genome phylogenetic analysis were performed to highlight transmission routes of the SCCmec and MRSA strain-specific lineages. Results In 2018, we isolated the MRSA JRA307 strain from the pus of a wound on a racehorse and the complete genome sequence suggests that it is a clinically relevant pvl-negative ST1-t127 MRSA that harbours both mecA and mecC on SCCmec-307. SCCmec-307 exhibited marked sequence identity to the previously reported SCCmec–mecC in the Staphylococcus sciuri GVGS2 strain isolated from cattle. The JRA307 mecC gene was classified as a mecC allotype of S. sciuri rather than that of Staphylococcus aureus. Conclusions We demonstrated the complete genome sequence of equine isolate JRA307, which is a clinically relevant MRSA harbouring mecA and mecC on SCCmec-307. The finding of mecC MRSA suggests a possible SCCmec transmission between distinct staphylococcal species. To the best of our knowledge, this is the first report of mecC detection in Japan.