Origin and evolution of the β-lactam resistance determinant in staphylococci

Abstract

In staphylococci, resistance to methicillin and to all β-lactam antibiotics is provided by the mecA gene, which encodes a penicillin-binding protein with low affinity to β-lactams (PBP2a). The mecA is carried by a mobile genetic element, the staphylococcal cassette chromosome mec (SCCmec), one of the most widely studied bacterial pathogenicity islands. SCCmec carries mecA and its regulators (the mec complex), as well as cassette chromosome recombinases encoded by ccr genes that form the ccr complex. These recombinases assure the mobility of the cassette. In addition, SCCmec cassettes carry joining regions (J regions) that link the orfX to the mec complex (J3); the mec complex to the ccr complex (J2) and the ccr complex to the end of the cassette (J1). The J regions can carry additional antibiotic resistance determinants, transposons, insertion sequences and plasmids. The SCCmec element always inserts at the same site in the bacterial chromosome, downstream orfX (which encodes a RNA methyltransferase), located 500 kb downstream the origin of replication. SCCmec is a very diverse element; so far eleven different types have been identified in Staphylococcus aureus and many more are probably carried by coagulase-negative staphylococcal species. SCCmec is transferred horizontally among strains and species of Staphylococcus, through an unknown molecular mechanism.info:eu-repo/semantics/publishedVersio