Staphylococcal Cassette Chromosome mec (SCCmec) Analysis of MRSA

Abstract

Methicillin-susceptible S. aureus (MSSA) changes to methicillin-resistant S. aureus upon the acquisition of Staphylococcal Cassette Chromosome mec (SCCmec), a genomic island that encodes methicillin resistance. All SCCmec elements reported to date share four common characteristics: (1) carrying the mec gene complex (mec); (2) carrying the ccr gene complex (ccr); (3) being flanked by characteristic nucleotide sequences, inverted repeats, and direct repeats, at both ends; and (4) being integrated at the integration site sequence (ISS) for SCC, which is located at the 3′-end of orfX or at the extremity of the SCC element. SCCmec elements in S. aureus are classified into different types based on the combination of mec and ccr, which share variations, five classes in mec and eight in ccr. To date, at least 11 types of SCCmec elements have been identified. Regions other than mec and ccr within the SCCmec element are designated as “joining regions” (J-regions), which are classified into three subgroups, J1-3. Many J-region variants have been identified among the SCCmec elements of types I–V. We herein describe PCR methods to type SCCmec elements by first identifying the mec and ccr type, and then identifying genes in the J-regions.