Performance of a new chromogenic oxacillin resistance screen medium (Oxoid) in the detection and presumptive identification of methicillin-resistant Staphylococcus aureus.

A new chromogenic Oxacillin Resistance Screen Agar (ORSA; Oxoid) for the presumptive detection of methicillin-resistant Staphylococcus aureus (MRSA) was compared to a phenyl-mannitol-salt-oxacillin medium (MS-Oxa), blood agar and brain heart-infusion (BHI) on 579 clinical specimens. After 24 h [48h] sensitivity and specificity for ORSA vs. MS-Oxa were 50.8% [68.2%] vs. 53.8% [65.7%] and 95.6% [94.5%] vs. 92.7% [91.8], respectively. Within 24 h, ORSA and MS-Oxa identified 51% and 54% MRSA. It is not feasible to omit BHI in MRSA-screening protocols since 33% MRSA grew in BHI only.