Minimal Inhibitory Concentration of Vancomycin in Staphylococcus aureus strains Isolated from Hospitalized Patients Versus Those Recovered from Out Patients

Staphylococcus aureus (S.aureus) is one of the most prevalent causes of nosocomial infections. It is also involved in community acquired infections. The resistance of this bacterium towards methicillin which has been reported since 1961, made Vancomycin the last choice for treatment of Staphylococcal infections.Considering the reduced sensitivity or resistance to vancomycin which has been observed since 1996, this study was conducted with the aim of evaluating the vancomycin MIC values (Minimun Inhibitory Concentration) of S. aureus cells isolated from hospitalized patients and compared with those recovered from outpatients. A cross sectional – analytic survey was conducted from 2006 till 2007. A total of 200 S.aureus strains were isolated from various clinical sources including blood, sputum, urine and sinus secretions. Their susceptibilities to vancomycin were initially surveyed by disk diffusion method. Subsequently, the MIC values of each individual strain towards vancomycin were determined by E-test strips, and the obtained data was analyzed by SPSS (V. 11) software. For statistical analysis, t-test was used. In 125 S. aureus strains isolated from hospitalized patients, the growth inhibition zones were 14-18 mm and the MIC values were 1-2mg/ml. In 75 S. aureus strains isolated from outpatients, the growth inhibition zones were 16-20 mm and the MIC values were 0.75-1.5 mg/ml. The result of this survey shows increased MIC values for vancomycin in hospitalized patients as compared to outpatients.