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Minimal inhibitory concentrations (MICs) and minimal bactericida/ concentrations (MBCs) for oxacillin and vancomycin on Staphylococcus aureus strains isolated from patients of the HUAP

Abstract

A total of 80 Staphylococcus aureus strains, isolated from patients of the Hospital Universitário Antônio Pedro - HUAP, were investígated for their in vitro susceptibílíties (MICs and MBCs) for oxacillin and vancomycin, by a twofold dilution method. Our results can be summarized as follow. Oxacíllín exhíbíted a relativelly good activity, with MIC50 = O. 78 μgim/anda MBC50 = 3.12 μgim/. Resístant strains to oxacillin (maximum M/C and MBC of, respectively: 200 and 800 μgim/) and tolerant ones (MBCIMIC >16) have been identified. Vancomycin, on the other hand, showed a 100% etficacy (maximum M/C and MBC of, respectívelly: 3.12 and 12.50 μgim/, with MIC90 = 1.56 μgim/ and MBC90 = 3.12 μgim/. No resistant neither tolerant strains to vancomycin were observed. These results suggest that, from the view-poínt of antibiotic therapy, oxacillin is sti/1 a suitab/e antíbiotíc agaínst S. aureus, íncluding tolerant straíns wíth MCBs below those concentratíons attainable at the infection sites. Whenever thís is not the case, oxací/lin should be replaced by vancomycín. ln such a sítuation, however, the clínicían should remain vigílant to vancomycín side ettects.