Comparison of methicillin resistance phenotype with mecA gene carriage in clinical isolates of Staphylococcus epidermidis

Coagulase negative، methicillin resistant Staphylococci specifically Staphylococcus epidermidis are important causes of nosocomial infections. In addition، most of these isolates show multi-resistance to a number of other antibiotics including β-lactams. In this study، methicillin resistance phenotype was compared to the presence of methicillin resistance gene (mecA gene) among the isolates. Fifty five clinical isolates collected from 3 hospitals in Tehran were tested for antibiotic susceptibility using disc diffusion and minimal inhibitory concentrations (MIC) were measured for meticillin using the broth microdilution assay. Presence of the mecA gene in the clinical isolates was detected using specific primers and PCR. The disk susceptibility results showed that 50isolates (90. 9 %) including 8 strains with intermediate inhibition zones were resistant to methicillin. MIC results showed 78. 1 % methicillin resistance with MIC values > 4 µg/ml. MIC results for the intermediately resistant isolates revealed 5 sensitive and 3 resistant strains. PCR results showed that all methicillin resistant isolates determined by disc diffusion and MIC assays carried the mecA gene except one isolate. Surprisingly، 4 isolates with methicillin sensitive phenotype contained the mecA gene as well. The results of this study suggest that presence of the mecA gene does not necessarily account for methicillin resistance. Ultimately، gene expression which is controlled by the environment، would determine the outcome.