Evaluation of MRSA Select, a new chromogenic medium for the detection of nasal carriage of methicillin-resistant Staphylococcus aureus.

MRSA Select is a new chromogenic medium for the detection from clinical specimens of methicillin-resistant Staphylococcus aureus (MRSA) growing as pink colonies. Screening samples (n=666) taken from patients were spread onto MRSA Select, oxacillin resistance screening agar base (ORSAB), mannitol salt agar and an in-house medium containing tobramycin-colistin-fungizone (TCF). Ninety-nine samples were positive for MRSA on at least one selective medium. Sensitivity and specificity were >94% for all media provided that incubation was extended to 48 h for ORSAB and that a coagulase test was performed for ORSAB and TCF. By contrast, on the single criterion of the colour of colonies for MRSA positivity, the specificity and sensitivity of MRSA Select were high (99.8% and 99%, respectively).