Validation of rapid screening tests for the identification of methicillin resistance in staphylococci

The Velogene Rapid MRSA Identification Assay (Alexon-Trend Inc., Ramsey, MN), a commercially available 90-min genotypic test using a chimeric probe for the cycling-mediated recognition of the mecA gene in staphylococci, was compared with the MRSA-Screen latex agglutination test, a 15-min phenotypic test (Denka Seiken Co., Tokyo, Japan) for the identification of the mecA gene product PBP 2a. The results of both techniques were compared with mecA gene PCR. A total of 210 stock-culture strains were tested, consisting of 108 methicillin-susceptible Staphylococcus aureus (MSSA) strains and 92 methicillin-resistant S. aureus (MRSA) strains. The performance of the assays was good, displaying sensitivities and specificities for Velogene and MRSA Screen of 96.7% and 100% and 96.7% and 100%, respectively. Both Velogene and MRSA Screen could not correctly identify three of the MRSA strains each. Repeat testing with a larger inoculum or exposure of the three distinct strains to methicillin, respectively, resolved these problems. All MSSA strains as well as the other genera were correctly addressed by both techniques. The 10 methicillin-resistant Staphylococcus epidermidis strains were detected by both techniques. Both the Velogene and the MRSA Screen assays accurately identified mecA-positive staphylococcal strains and can be successfully used for routine application in clinical microbiology laboratories.