Abstract

ABSTRACTOver a period of one year, 1986–1987, 116 strains of Staphylococcus aureus were isolated from patients attending two outpatient dermatology clinics in Houston, Texas. The purpose of this study was to evaluate the adequacy of routine antibiotic sensitivity testing methods for detecting methicillin-resistant Staphylococcus aureus (MRSA). The Kirby-Bauer disk diffusion method was compared with a commercially available screening medium containing 6 μg/ml of oxacillin and 4% NaCl. The minimal inhibitory concentration (MIC) of methicillin and 4% NaCl. The minimal inhibitory concentration (MIC) of methicillin, oxacillin with 4% NaCl to S aureus using the agar dilution method was lao determined. Approximately 90% of S aureus strains produced β-lactamase and were resistant to penicillin and ampicillin. By disk diffusion, no strains were resistant to methicillin, though diameters of zones of inhibition were between 10 and 14 mm in seven strains. All strains provided to be sensitive to methicillin by MIC determinations and on the oxacillin-NaCl screening medium. The MIC of methicillin was 2.5 μ/ml for the majority of strains of S aureus, between 0.16 and 0.31 μg/ml for oxacillin, and 0.08 to 0.16 μg for oxacillin with 4% NaCl. We concluded that the incidence of MRSA in an outpatient dermatology population is low, and a combination of disk diffusion of oxacillin-NaCl screening is adequate for testing sensitivity.