In Vitro Susceptibility of Methicillin-Resistant Staphylococcus aureus Isolates to Vancomycin, Teicoplanin, Linezolid, Quinupristin-dalfopristin and Daptomycin

Abstract

In this study, vancomycin, teicoplanin, linezolide and daptomycin susceptibility rates of 67 methicillin-resistant Staphylococcus aureus (MRSA) isolates obtained from various clinical samples between November 2006 and August 2010 in our laboratories, were investigated by E-test method and MIC values of the drugs were determined. Seventeen (25%) of the samples were from outpatient wards, 50 (75%) from inpatients of which 24 (48%) were from intensive care units. Distribution of MRSA isolated clinical samples were as follows: 16 (23.4%) blood, 28 (42.2%) wound swab, 15 (21.8%) tracheal aspirate, 2 (3.1%) urine, 2 (3.1%) urethral discharge, and one for each (1.6%) cerebrospinal fluid, joint fluid, catheter tip and nasal swab. Except one (1.5%) which was probably intermediate-resistant to vancomycin (since not confirmed by microdilution test or population analysis, this isolate was considered as "probable" intermediate-resistant), all of the isolates were found susceptible to all tested antibiotics. MIC(50) and MIC(90) values were determined as 0.75 and 1.5 µg/ml for vancomycin, 2 and 3 µg/ml for teicoplanin, 0.38 and 0.5 µg/ml for linezolide and 0.094 and 0.19 µg/ml for daptomycin, respectively. The MIC ranges were 0.25-3 µg/ml for vancomycin, 0.125-4 µg/ml for teicoplanin, 0.094-3 µg/ml for linezolide and 0.047-0.25 µg/ml for daptomycin. There was no statistically significant difference between MICs of outpatient, inpatient and intensive care unit isolates for any of the tested drugs (p> 0.05). Based on MIC90 values, daptomycin seems 4-16 times more effective than the other three drugs. It was concluded that considering their in-vitro antibacterial activity, these antibiotics can be used as alternatives to each other for the treatment of MRSA infections.