Introduction: Antimicrobial resistance among strains of Streptococcus pneumoniae, Haemophilus influenza, and Streptococcus pyogenes has limited the usefulness of conventional agents for the treatment of some infectious diseases related with these microorganisms. There is thus a clear need for new antimicrobial agents active against these resistant strains.
Objectives: To assess the in vitro susceptibility to telithromycin and other oral antimicrobial agents of 307 strains of S. pneumoniae, H. influenzae, and S. pyogenes with acquired mechanisms of resistance to macrolides and/or beta-lactams.
Methods: Antimicrobial susceptibility testing was performed by the agar dilution method, and results were preferentially evaluated according to National Committee for Clinical Laboratory Standards (NCCLS) guidelines.
Results: The activity of telithromycin against erythromycin-resistant S. pneumoniae was excellent. All the strains were inhibited with 2 mg/l, regardless of the mechanism of macrolide resistance exhibited. Telithromycin was slightly more active than the tested macrolides in beta-lactamase-producing H. influenzae strains, with a MIC90 of 2 mg/l. Telithromycin also demonstrated potent activity against macrolide-resistant S. pyogenes. The MIC of telithromycin was > 4 mg/l for only one out of the 202 tested strains.
Conclusions: Telithromycin is a very promising therapeutic option against bacterial pathogens of the respiratory tract, including strains that have developed mechanisms of resistance to macrolides and/or beta-lactams.