Tehran University of Medical Sciences Iranian Journal of Microbiology 2008-3289 8 3 2016 10 04 161 167 EN Sareh Sadat Hosseini Department of Microbiology, School of Medicine, Shahed University, Tehran, Iran Mohammad Niakan Department of Microbiology, School of Medicine, Shahed University, Tehran, Iran Horieh Saderi Molecular Microbiology Research Center, School of Medicine, Shahed University, Tehran, Iran Mitra Motallebi Department of Microbiology, School of Medicine, Tehran University of Medical Sciences, Tehran, Iran Morovat Taherikalani Razi Herbal Medicines Research Center & Department of Microbiology, School of Medicine, Lorestan University of Medical Sciences, Ilam, Iran Khairollah Asadollahi Department of Social Medicine, School of Medicine, Ilam University of Medical Sciences, Ilam, Iran Mohammad Emaneini Department of Microbiology, School of Medicine, Tehran University of Medical Sciences, Tehran, Iran 2016 01 12 2016 04 23 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.   https://ijm.tums.ac.ir/index.php/ijm/article/view/884 https://ijm.tums.ac.ir/index.php/ijm/article/download/884/607