Oxacillin susceptibility testing of Staphylococcus saprophyticus using disk diffusion, agar dilution, broth microdilution, and the Vitek GPS-105 card.

Eighty-three mecA negative isolates of S. saprophyticus had oxacillin zone diameters <or= 15 mm or MICs ranging from <or= 0.25-1.0 microg/ml when tested by either agar dilution, broth microdilution, or the Vitek GPS-105 card. Greater than 90% of these isolates would be considered resistant using NCCLS M7-A5, M100-S10 criteria. These results suggest that the current NCCLS MIC and zone diameter breakpoints for oxacillin resistance in coagulase-negative Staphylococci are not appropriate for S. saprophyticus as they do not correlate with the presence of the mecA gene.