Cefoxitin disc test as a marker for detecting methicillin resistance in Staphylococcus aureus isolates

S.aureus is an important cause of nosocomial infections. It has overcome most of the therapeutic agents, of which the most important problem for the physicians and the microbiologists is the emergence of MRSA. In the present study, an effort has been made to detect and compare the efficacy of the cefoxitin disc diffusion test with other phenotypic methods like oxacillin disc diffusion, oxacillin agar screening test and determination of MIC and to the genotypic detection of mec A and/em B genes using multiplex PCR. Oxacillin disc diffusion test identified 85(32.44%) strains as methicillin resistant, from oxacillin agar screening 80(30.53%) were found to be methicillin resistant, whereas cefoxitin disc diffusion test detected 79(30.15%) strains to be methicillin resistant. On estimation of MIC 79 strains were found to be methicillin resistant with MIC value ≥4 μg/ml.mec A and fem B genes were present in all the 79 strains detected as methicillin resistant by cefoxitin disc diffusion test and by the estimation of MIC. Cefoxitin disc diffusion test was found to be the most sensitive and specific phenotypic method of detection of methicillin resistance comparable to the detection of mec A and fern B genes.