A Novel Assay for Detection of Methicillin-ResistantStaphylococcus aureusDirectly From Clinical Samples

The timely detection of Methicillin-resistantStaphylococcus aureus(MRSA) is crucial for antimicrobial therapy and a key factor to limit the hospital spread of MRSA. Currently available commercial MRSA detection assays target the 3 ' end of theorfXgene and the right extremity of Staphylococcal Cassette Chromosomemec(SCCmec). These assays suffer from both false positive due to SCC-like elements that lackmecAand false negative results due to the inability to detect new or variant SCCmeccassettes with the existing primers. We developed a novel MRSA detection scheme, designed to circumvent issues present in the existing commercial assays. Our assay demonstrated specificity and accuracy, capable of detecting prototypic strains of SCCmectypes I-XIII [C(t) values ranged 8.58-26.29]. Previous false positive isolates (N= 19) by Xpert MRSA nasal assay were accurately classified with our assay. Further validation with 218 randomly selected clinical isolates (73 MRSA, 75 MSSA, 43 MR-CoNS, and 27 MS-CoNS) confirmed its feasibility and practicality. Testing assay performance with 88 direct clinical swabs from 33 patients showed that the assay was 96.6% in agreement with clinical culture results. Our novel MRSA detection assay targets both theS. aureusspecific sequence and themecA/mecCgenes simultaneously to overcome the false positive and false negative deficits of currently available commercial assays. The results validate our assay and confirmed its feasibility and practicality. The assay is not affected by SCCmectypes and only needs modification if newmechomologs emerge and establishes a new platform for other emerging SCCmectypes.