EVALUATION OF SCREENING AND COMMERCIAL METHODS FOR DETECTION OF METHICILLIN RESISTANCE IN COAGULASE-NEGATIVE STAPHYLOCOCCI

The National Committee for Clinical Laboratory Standards recommends 48 h of incubation by the oxacillin salt agar screen (OSAS) method for t he detection of methicillin-resistant coagulase-negative staphylococci (CoNS). An earlier identification of methicillin resistance is desira ble. The time to detection of the mecA gene by PCR was compared with t he times to detection by OSAS, by the oxacillin disk diffusion (ODD) m ethod, and with MicroScan Gram Positive Combo type 6 panels (MicroScan Inc. Sacramento, Calif.) and Vitek GPS-SA cards (bioMerieux Vitek Inc ., Hazelwood, Mo.). The combination of the Vitek card and the ODD meth od detected 92 of 99 methicillin-resistant strains of CoNS at 24 h; ho wever, 6 mecA-positive strains were phenotypically methicillin suscept ible. We conclude that most methicillin-resistant CoNS can;be detected and the results can be reported after overnight incubation by a combi nation of methods.