Determining the prevalence of methicillin- and vancomycin-resistant Staphylococcus aureus by MIC and E-Test

Staphylococcus aureus infection pervasively occurs in communities and hospitals and observing related guidelines is essential in preventing development of antibiotic resistance in Hospitals. In this study we tried to determine the prevalence of Methicillin and vancomycine resistant staphylococcus aureus (MRSA & VRSA) and find the most suitable diagnostic tool and treatment in affected patients. This study was performed on hospitalized patients in Sina Hospital in Tehran, Iran during 2009-2010. Eighty-five staphylococcus aureus samples were evaluated for resistance to oxacillin and vancomycine by both disc diffusion and E-test methods. The study population included 46 male and 39 female patients. The mean age of the participants was 51.46±19.21 years. The MRSA frequency was 50%. 67 (78.8%) patients had hospital-acquired staphylococcus infection. The rate of hospital-acquired MRSA was 93%. Length of hospital stay, undergoing invasive methods, history of antibiotic use three months prior to hospitalization and its kind were recognized as MRSA risk factors. There were no reports of VRSA except one case of vancomycine-intermediate S. aureus (VISA). The results of disk effusion and E-test methods were consistent. Considering the prevalence of methicillin resistance in hospital-acquired infections, it seems that oxacillin should not be used as the first-line option for empiric therapy against S. aureus till antibiogram results are available. Disc diffusion can also be reliably used instead of the more expensive E-test.