Description:
<jats:p><i>Background:</i> Telithromycin is a new ketolide increasingly used in Europe and the United States. Only very few telithromycin-resistant isolates have been described to date. <i>Methods:</i> The anti-pneumococcal activity of telithromycin was determined against four clinical isolates of <i>Streptococcus pneumoniae</i> with reduced susceptibility to telithromycin by time-kill methodology. <i>Results:</i> All four telithromycin non-susceptible strains had the constitutive macrolide-lincosamide-streptogramin B phenotype and the <i>erm</i>B genotype. Pneumococcal strains had telithromycin minimum inhibitory concentrations (MICs) ranging between 2 and 8 µg/ml. Mulitlocus sequence typing and serotyping showed three isolates to harbour the identical serotype (serotype 14) and sequence type (sequence type 143) indicating a genetic relatedness of strains. Telithromycin was only bactericidal against the isolates with telithromycin resistance, with 4–8 times the MIC after 24 h. <i>Conclusion:</i> The killing by telithromycin of <i>S. pneumoniae </i>isolates having an <i>erm</i>B resistance determinant and a telithromycin MIC of ≧2 µg/ml is slow. Achievable concentrations in serum, alveolar macrophages and epithelial lining fluid are below the concentrations which are necessary for bactericidal killing of highly telithromycin-resistant strains.</jats:p>