A simple and expedient PCR format for rapid molecular screening of methicillin-resistant Staphylococcus aureus in Amies gel swabs.

Screening patients for carriage of methicillin-resistant Staphylococcus aureus (MRSA) is commonly undertaken in hospital laboratories using phenotypic methods. This work is labour-intensive, costly and may take several days to complete. We report on the validation of a novel rapid screening approach for direct testing of Amies gel swabs for MRSA. The method is based on two quantitative real time-PCR (qRT-PCR) assays for the detection of the nuc and mecA genes of MRSA. Based on SYBR Green technology, the assays use significantly less reagents than conventional qRT-PCR methods and are applied to testing templates derived directly from aqueous suspensions of swabs. Notwithstanding the occurrence of false-positives due to non-specific fluorescence generated by the SYBR Green dye, the novel assays showed a high negative predictive value enabling earlier reporting of negative findings and selection of swabs for confirmatory phenotypic testing for MRSA. In a blinded trial of 461 swabs, of which 34 (7.4%) were previously shown to be culture-positive for MRSA, the novel assays selected 121 (26.2%) swabs (inclusive of the known MRSA-positive swabs) for phenotypic testing. This enabled early reporting of negative findings for 340 (73.8%) of the 461 swabs tested. Application of this method has implications for screening strategies for large laboratories whilst achieving cost benefits.