مطالعه حساسيت سويه هاي استافيلوكوكوس اورئوس ايزوله شده از نمونه هاي باليني در برابر وانكومايسين با استفاده از روش E-test در تبريز

Sensitivity of Staphylococcus aureus Strains Isolated from Clinical Specimens against Vancomycin by Using E-test in Tabriz

Background and Objectives: Vancomycin has been widely used in the treatment of infections caused by Methicillin-resistant Staphylococcus aureus (MRSA). The emergence of vancomycin-intermediate S. aureus(VISA), heterogenous VISA (hVISA) and vancomycin resistant S. aureus (VRSA) in various parts of the world has been of great concern in clinical settings. This study was performed to evaluate the possible isolation of hVISA, VISA and VRSA strains in Tabriz, Iran. Materials and Methods: One hundred S. aureus isolates were collected from in-patients in Tabriz between September 2005 and July 2006. All of the collected isolates were identified using Gram staining, coagulase, catalase and DNase tests. MICs of our isolates were determined against vancomycin by E.test and disk diffusion method was also applied and the results were compared. For detection of hVISA strains we used the population analysis method . Results: Ninty eight percent of the S. aureus isolates were sensitive to vancomycin and MICs of the isolates were between 1.5-3 μg/ml. We encountered two isolates with MIC=4 μg/ml, which subsequent population analysis confirmed to be hVISA, i.e. the MIC increased to ≥ 8 μg/ml. In disk agar sensitivity tests using 11 antibiotics the following sensitivity results were obtained: vancomycin (100%), rifampin (100%), ciprofloxacin (100%), cotrimoxazole (100%), cephalothin(74%), methicillin (62%), chloramphenicol (44%), clindamycin (43%), gentamicin (36%), erythromycin (31%) and penicillin G(1%). Conclusion: Our results showed that 98% of the isolates were sensitive to vancomycin and 2% of them were hVISA. Therefore vancomycin could still be used as a valuable drug for treatment of S. aureus infections. The detection of 2% hVISA in 100 clinical specimens in our study and worldwide increasing resistance to vancomycin and other glycopeptides in S. aureus clinical isolates indicate importance of antibiotic-sensitivity testing and MIC determination in S. aureus isolates from clinical specimens