VANCOMYCIN RESISTANCE AMONG CLINICAL ISOLATES OF STAPHYLOCOCCUS AUREUS

Background: Vancomycin has been widely used in the treatment of infections caused by methicillin-resistant Staphylococcus aureus (MRSA). The emergence of vancomycin-intermediate and -resistant Staphylococcus aureus (VISA and VRSA, respectively) in various parts of the world has been of great concern in clinical settings. This study was performed to evaluate the possible presence of VISA and VRSA in Tehran, Iran. Methods: The minimum inhibitory concentration (MIC) of vancomycin for 139 Staphylococcus aureus strains isolated between April and August 2003 was carried out according to the standards of the National Committee for Clinical Laboratory Standards (NCCLS) using the agar dilution method. Resistance of VRSA to vancomycin was checked by E-test. Disk diffusion method was also used to determine the susceptibility of strains to common antibiotics. Determination of oxacillin MIC was performed for VRSA with the agar dilution method according to the guidelines of NCCLS and the E-test. Results: Using the disk diffusion test, most isolates (91.7%) were resistant to penicillin while the lowest resistance (10.9%) was to imipenem. Five of the 139 isolates had a vancomycin MIC of ≥ 128 by agar dilution and E-test methods. All VRSA isolates were MRSA (MIC ≥ 256) and the majority were also highly resistant to other examined antibiotics. Conclusion: This is the first report of isolation of VRSA in Tehran, which calls for confirmation by reference laboratories and further epidemiological studies.