mecALocus Diversity in Methicillin-Resistant Staphylococcus aureusIsolates in Brisbane, Australia, and the Development of a Novel Diagnostic Procedure for the Western Samoan Phage Pattern Clone

ABSTRACTAn emerging public health phenomenon is the increasing incidence of methicillin-resistant Staphylococcus aureus(MRSA) infections that are acquired outside of health care facilities. One lineage of community-acquired MRSA (CA-MRSA) is known as the Western Samoan phage pattern (WSPP) clone. The central aim of this study was to develop an efficient genotyping procedure for the identification of WSPP isolates. The approach taken was to make use of the highly variable region downstream of mecAin combination with a single nucleotide polymorphism (SNP) defined by the S. aureusmultilocus sequence typing (MLST) database. The premise was that a combinatorial genotyping method that interrogated both a highly variable region and the genomic backbone would deliver a high degree of informative power relative to the number of genetic polymorphisms interrogated. Thirty-five MRSA isolates were used for this study, and their gene contents and order downstream of mecAwere determined. The CA-MRSA isolates were found to contain a truncated mecAdownstream region consisting of mecA-HVR-IS431 mec-dcs-Ins117, and a PCR-based method for identifying this structure was developed. The hospital-acquired isolates were found to contain eight different mecAdownstream regions, three of which were novel. The Minimum SNPs computer software program was used to mine the S. aureusMLST database, and the arcC272G polymorph was identified as 82% discriminatory for ST-30. A real-time PCR assay was developed to interrogate this SNP. We found that the assay for the truncated mecAdownstream region in combination with the interrogation of arcCposition 272 provided an unambiguous identification of WSPP isolates.