frequency of genes encoding erythromycin ribosomal methylases among staphylococcus aureus clinical isolates with different d-phenotypes in tehran, iran

background and objectives: macrolide, lincosamide and streptogramin type b (mlsb) antibiotics are important in the treatment of staphylococcus aureus infections and existence of isolates with ability to resist against mlsb antibiotics is worrisome. materials and methods: in this cross sectional study, 101 s. aureus isolates were collected from patients of five selected hospitals in tehran over a period of five months. disk diffusion tests and differentiation between constitutive and inducible resistances were carried out by d-test. the presence of meca, msra, erma and ermc genes were detected using pcr or multiplex pcr. results: out of 101 s. aureus isolates, 58 (57.4%) were methicillin resistant and 57 (56.4%) expressed resistance to erythromycin. the prevalence of constitutive mlsb (cmlsb), inducible mlsb (imlsb) and ms (negative) phenotype in all erythromycin resistant isolates were 71.9, 26.3 and 1.7%, respectively. out of all the erythromycin resistant isolates, 57.8% harbored both erma and ermc genes which possessed constitutive resistance. 8.7% of the isolates contained erma gene alone which possessed inducible resistance with d phenotype and 5.2% of isolates just contained ermc gene which had inducible resistance with d+ phenotype. msra gene was detected in 3.5% of the erythromycin resistant s. aureus isolates with constitutive resistance. none of the genes were detected among ms phenotypes. conclusion: in this study, most of s. aureus isolates carried both erma and ermc genes and there was a significant relationship ( p value ≤ 0.05) between different resistance phenotypes and erm genes. keywords: staphylococcus aureus , d-test, erm a, ermc, msra