Vancomycin sensitivity of Staphylococcus aureus isolates from hospital patients in Karachi, Pakistan

Methicillin-resistant Staphylococcus aureus (S. aureus) (MRSA), resistant to all antibiotics including Vancomycin, has been reported in Japan, USA, Canada and Brazil. Hence, the main objective of this study was to evaluate the possible presence of Vancomycin resistant or intermediate S.aureus in Karachi. A total of 850 clinical isolates were collected from two civil hospitals in the city between February 2006 and January 2007. They were identified using standard bacteriological methods.Sensitivity to recommended antibiotics was determined by disc diffusion, agar dilution, and E-test quantitative minimum inhibitory concentration (MIC). Susceptibility to natural or semi-natural products was determined by the agar dilution method. Out of 850 isolates, 250 were MRSA, of which 22% were resistant to 4 µg/ml Vancomycin, 24% to 8 µg/ml, 15.2% to 16 µg/ml, 10% to 20 µg/ml, and 13.2% to 30 µg/ml; the remaining 15.6% were sensitive to all used concentrations. Although we did not detect any Vancomycin-resistant S. aureus (VRSA), we found that 13% of the strains were intermediates (VISA), i.e. resistant to 30 µg/ml of Vancomycin. Because of the continuously increasing prevalence of VISA, it is imperative to minimize the use of Vancomycin. Indeed, the drug should only be prescribed for the treatment of documented, culture-proven infections with MRSA that are not susceptible to routine or alternative agents. This should help avoid the consequences of the development of Vancomycin resistant S. aureus (VRSA) in our environment.