Detection of Methicillin ResistantStaphylococcus aureusand Determination of Minimum Inhibitory Concentration of Vancomycin forStaphylococcus aureusIsolated from Pus/Wound Swab Samples of the Patients Attending a Tertiary Care Hospital in Kathmandu, Nepal

Abstract

The present study was conducted to evaluate the performance of cefoxitin disc diffusion method and oxacillin broth microdilution method for detection of methicillin resistantS. aureus(MRSA), taking presence of mecA gene as reference. In addition, inducible clindamycin resistance and beta-lactamase production were studied and minimum inhibitory concentration (MIC) of vancomycin forS. aureusisolates was determined. A total of 711 nonrepeated pus/wound swab samples from different anatomic locations were included in the study. TheStaphylococcus aureuswas identified on the basis of colony morphology, Gram’s stain, and biochemical tests. A total of 110 (15.47%)S. aureusisolates were recovered, of which 39 (35.50%) isolates were identified as MRSA by cefoxitin disc diffusion method. By oxacillin broth microdilution method, 31.82% of theStaphylococcus aureusisolates were found to be MRSA. However, mecA gene was present in only 29.1% of the isolates. Further, beta-lactamase production was observed in 71.82% of the isolates, while inducible clindamycin resistance was found in 10% ofS. aureusisolates. The MIC value of vancomycin forS. aureusranged from 0.016 μg/mL to 1 μg/mL. On the basis of the absolute sensitivity (100%), both phenotypic methods could be employed for routine diagnosis of MRSA in clinical microbiology laboratory; however cefoxitin disc diffusion could be preferred over MIC method considering time and labour factor.