Phenotypic and Genotypic Methods for the Detection of Methicillin Resistant Coagulase Negative Staphylococci : A Comparative Study.

CONS are the major cause of nosocomial infection in last decade and methicillin resistant CoNS has emerged as a major clinical problem. The present study was to compare different phenotypic methods with genotypic method PCR, for the detection of methicillin resistance in CoNS. 100 CoNS isolates from different samples were studied for the detection of mecA gene. PCR was considered as “gold standard”. Oxacillin and cefoxitin antibiotics were used for different phenotypic tests (DD, Agar dilution and MHOX). The sensitivities of oxacillin and cefoxitin disks for all CONS were found to be 92.30% and 88.46% respectively and the specificities were 87.5% and 100% respectively. The sensitivities of the agar dilution test for oxacillin and cefoxitin were 86.53% and 80.76%, respectively, where as the specificities were 79.16% and 85.41%, respectively. The sensitivity of MHOX was observed to be 96.16% and specificity 72.91%. Cefoxitin D.D and oxacillin AD methods could be used as initial test for the determination of methicillin resistance in CoNS isolates. The result of MHOX shows that it could be the best single method for the evaluation of oxacillin resistance mediated by the mec A gene for all CoNS species.