Genotypic characterization of macrolide-resistant strains of Streptococcus pneumoniae isolated in Quebec, Canada, and in vitro activity of ABT-773 and telithromycin.

Increasing resistance of Streptococcus pneumoniae to macrolides represents a challenge for clinicians. New ketolides have an enhanced activity against macrolide-resistant strains. Four hundred and seventy-four strains of S. pneumoniae were collected during the 2000-2001 season in Quebec through a surveillance network. Macrolide resistance was 20.2%, and significantly higher in non-invasive strains versus invasive ones (22.4% versus 14.8%), and in children (30%) versus adults (14.8%). For susceptible strains, MIC(90)s of ABT-773 and telithromycin were 0.008 and 0.015 mg/L. Among the 96 macrolide-resistant strains, 56 (58%) were erm(B), 35 (37%) carried the mef(A) gene, four were carrying both genes and one none. ABT-773 and telithromycin were very active against all these resistant strains irrespective of the resistance mechanism, with MIC(90)s of 0.25 and 0.5 mg/L, respectively.