Characterization of macrolide resistance in Streptococcus pyogenes: prevalence, phenotype and genotype

The increase in macrolide resistance among Streptococcus pyogenes isolates is a cause to be concerned. To investigate the macrolide resistance trends, phenotypes and genotypes, we examined 40 clinical isolates of Group A Streptococcus (GAS) collected between 2013 and 2014. Susceptibilities to macrolide antimicrobial agents were determined by disk diffusion method and inducible clindamycin resistance was identified using D-zone test. Beside, macrolide resistance genes were detected by polymerase chain reaction (PCR). The rates of resistance to erythromycin, azithromycin, clindamycin and clarithromycin were 20%, 20%, 15%, 10% respectively. None of the isolates exhibited resistance to penicillin. Among 8 erythromycin-resistant Streptococcus pyogenes isolates 4 had an M phenotype and 4 had an MLSB phenotype (3 cMLSB and 1 iMLSB). The isolates with cMLSB and iMLSB phenotype had ermA and ermB gene, respectively. Of 16 macrolide-resistant GAS isolates, 5 (31%) harbored the ermB gene and 1 (6%) the ermA. Also, one isolate without any macrolide resistance was positive for ermB gene. We found a high level of macrolide resistance in Streptococcus pyogenes in Iran. Moreover, clindamycin and clarithromycin would be the drugs of choice for treating penicillin-allergic patients. The phenotypes of erythromycin resistance seem to be associated with certain erm genotypes in Streptococcus pyogenes isolates.