A selective broth enrichment combined with real-time nuc-mecA-PCR in the exclusion of MRSA

Abstract

We analyzed the performance of a selective enrichment broth combined with Taqman-based real-time duplex nuc-mecA-PCR to expedite the screening of methicillin-resistant Staphylococcus aureus (MRSA). We found the broth to be able to select MRSA strains (oxacillin MIC range 4-256 microg/ml) from MSSA strains. A total of 31 MRSA strains were found from 1250 clinical samples screened. The nuc-mecA-PCR was positive from all enrichment broths containing MRSA. From the remaining 1219 samples negative for MRSA on culture/subculture, 138 samples were nuc+/mecA+ in PCR. The sensitivity of the test was 93.5%, specificity 88.6%, positive predictive value 17.3%, and negative predictive value 99.8% as compared to culture. Thus, with this method, the negative MRSA results can be reliably reported within 24-48 h from sampling. The method is a practical additional alternative to those already described for the same purpose.