Activity of ceftibuten, cefaclor, azithromycin, clarithromycin, erythromycin and telithromycin against Streptococcus pyogenes clinical isolates with different genotypes and phenotypes

Background: The growing number of macrolide-resistant strains of Streptococcus pyogenes represents an increasing worldwide problem. Macrolide resistance in S. pyogenes is mediated by several different genes, which determine different levels of resistance to macrolides, lincosamides and streptogramin B (MLS). Methods:This study compared the in vitro antimicrobial activity of azithromycin, clarithromycin, erythromycin, ceftibuten, cefaclor, and telithromycin against 287 strains of S. pyogenes by the broth microdilution method. All strains were characterized both phenotypically and genotypically for erythromycin resistance and most of them have been M-typed by means of PCR. Results: Ceftibuten and cefaclor showed the best antimicrobial activity, while MIC values for telithromycin were higher against constitutively MLS (cMLS)-resistant strains rather than against the other phenotypes. Conclusion: Oral cephalosporins retain the best activity against S. pyogenes; showing good activity except for cMLS-resistant strains, telithromycin is a valid alternative to these antimicrobials.