A STRATEGY FOR RAPID IDENTIFICATION OF METHICILLIN RESISTANT STAPHYLOCOCCUS AUREUS NASAL CARRIER STATUS.

Methicillin Resistant Staphylococcus aureus (MRSA) is a multi drug resistant organism responsible for severe outbreaks of life threatening infections in hospitals which are difficult to treat They are spread by nasal carriage among the hospitalised patients, staff and visitors. Mannitol cloxacillin salt agar (MCSA) is a single tube method to identify MRSA. However, tubes showing growth and change in colour on biochemical characterisation often do not prove to be MRSA. In this study we have combined two strategies for the rapid identification and isolation of MRSA by culture in MCSA and multiplex PCR for mecA and femB genes. Anterior nasal swabs obtained from nursing staff and patients admitted to a large referral hospital, were inoculated into MCSA. Of the 100 tubes inoculated, 8 tubes showed change in colour and growth. On conventional testing 4 were MRSA, 3 were methicillin sensitive S aureus (MSSA) and 1 was Methicillin Sensitive Coagulase Negative S aureus (MSCNS). Genotyping by multiplex PCR revealed 5 MRSA, 2 MSSA and 1 MRCNS. The Multiplex PCR technique to rapidly identify presence of mecA and femB genes showed presence of both mecA and femB bands in all MRSA. The methicillin sensitive organisms showed absence of mecA gene while coagulase negative organisms showed absence of the fern B gene. Combining MSCA with multiplex PCR for mec A and fem B genes made the test both rapid and specific. Use of this strategy would enable rapid screening of nasal carriers and early implementation of hospital infection control measures.