Novel Multiplex PCR Assay for Characterization and Concomitant Subtyping of Staphylococcal Cassette Chromosome mec Types I to V in Methicillin-Resistant Staphylococcus aureus

Abstract

Staphylococcal cassette chromosome mec(SCC mec) typing is essential for understanding the molecular epidemiology of methicillin-resistant Staphylococcus aureus(MRSA). SCC mec elements are currently classified into types I to V based on the nature of the mec and ccr gene complexes, and are further classified into subtypes according to their junkyard region DNA segments. Previously described traditional SCC mec PCR typing schemes require multiple primer sets and PCR experiments, while a previously published multiplex PCR assay is limited in its ability to detect recently discovered types and subtypes such as SCC mec type V and subtypes IVa, b, c, and d. We designed new sets of SCC mec type- and subtype-unique and specific primers and developed a novel multiplex PCR assay allowing for concomitant detection of the methicillin resistance (mecA gene) (also serving as an internal control) to facilitate detection and classification of all currently described SCC mec types and subtypes I, II, III, IVa, b, c, d, and V. Our assay demonstrated 100% sensitivity and specificity in accurately characterizing 54 MRSA strains belonging to the various known SCC mec types and subtypes, when compared with previously described typing methods. Further application of our assay in 453 randomly selected local clinical isolates confirmed its feasibility and practicality. This novel assay offers a rapid, simple, and feasible method for SCC mec typing of MRSA, and may serve as a useful tool for clinicians and epidemiologists in their efforts to prevent and control infections caused by this organism.