Phenotypic and genotypic study of macrolide, lincosamide and streptogramin B (MLSB) resistance in clinical isolates of Staphylococcus aureus in Tehran, Iran

BACKGROUND Resistance to antimicrobial agents among Staphylococcus aureus is an increasing problem. Two common genes responsible for resistance to macrolide, lincosamide and streptogramin B (MLSB) antibiotics are the ermA and ermC genes. Three resistance phenotypes have been detected to these antibiotics: strains containing cMLSB (constitutive MLSB) and iMLSB (inducible MLSB), which are resistant to macrolide, lincosamide and streptogramin B antibiotics, and MS, which is only resistant to macrolide and streptogramin B antibiotics. The aim of this study was to determine the prevalence of MLSB phenotypes and genotypes in erythromycin-resistant strains of S. aureus isolated from patients in 4 university hospitals in Tehran, Iran. MATERIAL/METHODS S. aureus strains were isolated from various clinical specimens and identified by routine phenotypic methods and PCR for nuc gene. Erythromycin resistance was determined by disk diffusion testing. Prevalence of MLSB phenotypes was determined by use of the D-test. ermA and ermC genes were detected by PCR. RESULTS Altogether, 126 erythromycin-resistant strains of S. aureus were detected. Prevalence of cMLSB, iMLSB and MS resistance phenotypes were 92.8%, 6.4%, and 0.8%, respectively; 60.3% of strains had ermA gene and 54.8% ermC gene; 61 strains (48.4%) contained 2 studied erm genes and 42 strains (33.3%) did not have any studied erm genes. CONCLUSIONS Due to the high prevalence of clindamycin resistance among S. aureus isolated from patients in Iran, we recommend clindamycin therapy only after proper antimicrobial susceptibility testing.