In Vitro Activities of the Novel Ketolide Telithromycin (HMR 3647) against Erythromycin-Resistant Streptococcus Species

Abstract

The in vitro susceptibilities of 184 erythromycin-resistant streptococci to a novel ketolide, telithromycin (HMR 3647), were tested. These clinical isolates included 111 Streptococcus pyogenes , 18 group C streptococcus, 18 group G streptococcus, and 37 Streptococcus pneumoniae strains. The MICs for all but eight S. pyogenes strains were ≤0.5 μg/ml, indicating that telithromycin is active in vitro against erythromycin-resistant Streptococcus strains. All strains for which MICs were ≥1 μg/ml had an erm (B) resistance gene and six strains for which MICs were ≥4 μg/ml had a constitutive erm (B) gene (MIC range, 4 to 64 μg/ml). Interestingly, for S. pneumoniae strains with a constitutive erm (B) gene, MICs were ≤0.25 μg/ml (MIC range, ≤0.008 to 0.25 μg/ml). Our in vitro data show that for S. pyogenes strains which constitutively express the erm (B) methylase gene, MICs are so high that the strains might be clinically resistant to telithromycin.