Structure and specific detection of staphylococcal cassette chromosome mec type VII

Staphylococcal cassette chromosome mec (SCCmec) type VII, found in community-acquired methicillin-resistant Staphylococcus aureus belonging to multilocus sequence type (ST) 59 from Taiwan, was 41,347 bp in size and flanked by 19-bp attL and attR sequences. It was inserted into the att site at the 3′-end of orfX in the orfX-orfY (putative tRNA dihydrouridine synthase) region in ST59 S. aureus. The 5′-end side 9911-bp core region of SCCmecVII, which contained attL and the cassette chromosome recombinase gene (ccrC8), was shared by other SCC structures, SCCmercury and mosaic SCCmec from Switzerland, indicating its important role in SCC evolution. The central 21,245-bp core region contained mec complex (C2b) and another ccrC gene (ccrC2), and was highly homologous to SCCmecV, but with substitutions, insertion and replacement. The 3′-end side 10,191-bp sequence was unique. Therefore, SCCmecVII has emerged through recombination and insertion events. Multiplex and real-time PCR assays were developed for specific detection of SCCmecVII.