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.