Association of Erythromycin Resistance with the mefA and ermB Genes among Clinical Isolates of Streptococcus pneumoniae in Tehran, Iran

Introduction: Streptococcus pneumoniae is one of the major pathogens responsible for respiratory tract infections, meningitis, and bacteremia. In most countries around the world, an increase in the emergence of macrolide-resistant S. pneumoniae isolates has become a serious problem. Therefore, this study was conducted to investigate the association of erythromycin resistance with the mefA and ermB genes among clinical isolates of S. pneumoniae in Tehran City (Tehran Province, Iran). Materials and Methods: In this cross-sectional study, 62 erythromycin-resistant S. pneumoniae (ERSP) isolates were obtained from patients in four hospitals in Tehran city during 2013-2015. The macrolide resistance genes mefA and ermB were detected in ERSP isolates using polymerase chain reaction (PCR) assays. Furthermore, the copy number and expression level of the mefA gene were determined by real-time PCR. Results: In the present study, the overall resistance to erythromycin in S. pneumoniae isolates was 84.93% (62 isolates out of 73). Either mefA or ermB was identified in 10 (16.13%) and 36 (58.06%) ERSP isolates, respectively, and 7 (11.29%) ERSP isolates harbored both genes. Comparison of the mean relative expression of the mefA gene in ERSP isolates with different erythromycin minimal inhibitory concentration (MIC) values indicated that the expression level was increased approximately twofold for each doubling of the MIC value. Conclusion: Our findings highlighted the dominance of ribosomal methylation encoded by ermB as the most common mechanism of macrolide resistance in clinical S. pneumoniae isolates from Iran. Furthermore, in the present study, the expression levels of the mefA gene showed a significant increase in the ERSP isolates with higher erythromycin MIC values.