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 (Psi) staphylococcal cassette chromosome mec (SCCmec) elements. Integration site sequences for SCC flanked and subdivided composite Psi SCCmec(Epi0076A) (69569 bp) into Psi SCC1(Epi0076A)-Psi SCCmec(Epi0076A)-Psi SCC2(Epi0076A) and composite Psi SCCmec(KM0218) (24554 bp) into Psi SCCKM0218-Psi SCCmec(KM0218). Putative gamma-haemolysin genes (hlgB and hlgC) were found at the 3' end of both composite elements. Psi SCCmec(KM0218) contained a complete mecB gene complex (mecI(m)-mecR1(m)-mecB-blaZ(m)) downstream of a new IS21-family member (ISMaca1). Psi SCCmec(Epi0076A) carried a blaZ(m)-deleted mecB gene complex similar to that reported in 'Macrococcus goetzii' CCM4927(T). 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 Psi SCCmec(KM0218). 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.