Macrococcus canis contains recombinogenic methicillin resistance elements and the mecB plasmid found in Staphylococcus aureus

OBJECTIVES: To analyse the genetic context of mecB in two Macrococcus canis strains from dogs, compare the mecB-containing elements with those found in other Macrococcus and Staphylococcus species, and identify possible mobilizable mecB subunits. METHODS: Whole genomes of the M. canis strains Epi0076A and KM0218 were sequenced using next-generation sequencing technologies. Multiple PCRs and restriction analysis confirmed structures of mecB-containing elements, circularization and recombination of mecB subunits. RESULTS: Both M. canis strains contained novel composite pseudo (Ψ) staphylococcal cassette chromosome mec (SCCmec) elements. Integration site sequences for SCC flanked and subdivided composite ΨSCCmecEpi0076A (69569 bp) into ΨSCC1Epi0076A-ΨSCCmecEpi0076A-ΨSCC2Epi0076A and composite ΨSCCmecKM0218 (24554 bp) into ΨSCCKM0218-ΨSCCmecKM0218. Putative γ-haemolysin genes (hlgB and hlgC) were found at the 3' end of both composite elements. ΨSCCmecKM0218 contained a complete mecB gene complex (mecIm-mecR1m-mecB-blaZm) downstream of a new IS21-family member (ISMaca1). ΨSCCmecEpi0076A carried a blaZm-deleted mecB gene complex similar to that reported in 'Macrococcus goetzii' CCM4927T. A second mecB gene was found on the 81325 bp MDR plasmid pKM0218 in KM0218. This plasmid contained a complete Tn6045-associated mecB gene complex distinct from that of ΨSCCmecKM0218. pKM0218 was almost identical to the mecB-containing plasmid recently reported in Staphylococcus aureus (overall 99.96% nucleotide identity). Mobilization of mecB within an unconventional circularizable structure was observed in Epi0076A as well as chromosomal plasmid insertion via recombination of mecB operons in KM0218. CONCLUSIONS: Our findings provide evidence of both the continuing evolution of mecB-containing elements in macrococci and M. canis as a potential source of the mecB-containing plasmid found in staphylococci.