REVISED INTERPRETATION OF OXACILLIN MICS FOR STAPHYLOCOCCUS-EPIDERMIDIS BASED ON MECA DETECTION

In 1992 and 1993, at The Ohio State University Medical Center, a large r proportion of Staphylococcus epidermidis strains required oxacillin MICs of 1 to 2 mu g/ml than did Staphylococcus aureus strains. mecA ge notype was correlated with antimicrobial susceptibility for selected c linical S. epidermidis strains. All 14 strains that required oxacillin MICs of less than or equal to 0.25 mu g/ml and 2 of 5 strains that re quired oxacillin MICs of 0.5 mu g/ml were susceptible by 1-mu g/ml oxa cillin disk test and were mecA negative. Three of 5 strains that requi red oxacillin MICs of 0.5 mu g/ml and all 18 strains that required oxa cillin MICs of greater than or equal to 1.0 mu g/ml were resistant by oxacillin disk test and were mecA positive. Current National Committee for Clinical Laboratory Standards MIC interpretive criteria may under estimate methicillin resistance among S. epidermidis strains.