Preliminary evaluation of an automated commercial real time PCR assay for MRSA testing in a clinical microbiology laboratory (#237)
Studies have shown that surveillance for carriage of methicillin-resistant Staphylococcus aureus (MRSA) can significantly reduce the incidence of MRSA nosocomial infections. At Royal Perth Hospital we routinely perform nasal and throat colonisation screening using the BD GeneOhm™ MRSA ACP assay (GeneOhm). A new BD MRSA assay on the automated BDMax™ instrument is now available. This instrument utilises an efficient magnetic bead based extraction technique and a real time PCR amplification and detection that includes multiple primer sets and probes for improved MRSA identification. This study reports the initial evaluation of the BDMax™ MRSA assay (BDMax), on a selection of organisms. Three groups of isolates were tested using swabs inoculated with a 0.5 McFarland suspension of overnight cultures; 144 locally acquired, fully characterised, community-associated and hospital-associated MRSA strains, eight coagulase negative staphylococci and 16 methicillin-sensitive Staphylococcus aureus (MSSA). BDMax correctly identified 136/144 of the MRSA strains, including five MRSA strains previously not detected by the GeneOhm™ MRSA assay. All eight coagulase-negative staphylococci, including S.lugdenensis and S.epidermidis tested negative on the BDMax. Testing of MSSA, from a 1 x 10^4 cfu/ml suspension, yielded 15/16 not detected results. One MSSA was incorrectly identified as an MRSA by BDMax. This evaluation has demonstrated that the BDMax accurately detected 94.4% of the current MRSA strains seen in our local population which account for over 99% of MRSA isolated. The BDMax also demonstrated an improvement in MRSA identification by detecting 5 additional strains compared to the GeneOhm. One false positive result was reported from 24 non-MRSA isolates. A further evaluation of this assay, comparing it to culture, is currently being undertaken to determine the clinical performance.