LEVELS OF VANCOMYCIN SUSCEPTIBILITY AMONGST ISOLATED Staphylococcus aureus STRAINS IN A TERTIARY CARE HOSPITAL

Out of 260 strains isolated from the clinical specimens from different wards of hospital, 105 were identified as Methicillin resistant Staphylococcus aureus (MRSA). Minimum inhibitory concentrations (MIC) of vancomycin of these strains were determined by agar dilution method following CLSI guidelines. Sensitivity of different antibiotics was determined by Kirby Bauer disc diffusion method. Eight strains had MIC of vancomycin of 4 microgram /ml (μg/ml), 138 strains had MIC of 2 microgram /ml and 114 had MIC of 1 microgram/ml. All strains having MIC 4μg/ml were MRSA and were resistant to more than five antibiotics. Out of 138 strains having MIC of 2 μg/ml, 88 were MRSA and 50 were MSSA. Significant relation was found between increase in MIC of vancomycin and methicillin resistance. The most common risk factors associated with increased MIC of vancomycin were prior treatment of vancomycin and prolonged hospitalization.