Detection of methicillin-resistant Staphylococcus aureus (MRSA) from growth on mannitol salt oxacillin agar using PCR for nosocomial surveillance

This study evaluated a polymerase chain reaction (PCR) method for detection of methicillin-resistant Staphylococcus aureus (MRSA) in specimens referred for nosocomial surveillance. PCR was used to detect the mecA and nuc gene targets using yellow growth on mannitol salt agar containing 6 mg/liter oxacillin (MSO-6) as a source of DNA (N = 645). The diagnostic values for PCR compared with culture methods were 97% specificity, 100% sensitivity, 96% positive predictive value, and 100% negative predictive value. Total cost for PCR per test is $3.62 compared to $4.77 for culture. However, the total cost per specimen is significantly lower due to only 20% of all surveillance specimens producing yellow colonies on MSO-6. The average turnaround time for the PCR method is 48 h compared with 82 h for culture. PCR amplification of mecA and nuc genes using yellow colonies on MSO-6 is a simple, fast, accurate and cost-effective method for routine use in clinical laboratories for detecting MRSA in surveillance specimens.