Comparative activity of telithromycin against typical community-acquired respiratory pathogens

Respiratory tract infections (RTIs) remain a significant cause of morbidity and mortality. Major bacterial pathogens in RTIs, such as Streptococcus pneumoniae, have exhibited increasing resistance to a variety of antibiotics during the past decades. Telithromycin, the first ketolide, was designed especially to overcome this resistance. The present study was conducted to assess the comparative activity of telithromycin against typical RTI pathogens in Austria.

A total of 1,015 bacterial isolates was tested, including S. pneumoniae, Streptococcus pyogenes, Staphylococcus aureus and Haemophilus influenzae. MICs of the following antimicrobials: penicillin G, ampicillin (for H. influenzae), azithromycin, clarithromycin, erythromycin A and telithromycin were determined using the NCCLS broth microdilution method.

Telithromycin showed excellent activity against S. pneumoniae, with 99.8% of all isolates being susceptible. Penicillin remained active with an MIC50 and MIC90 of 0.007 mg/L. Nevertheless, a notable increase in penicillin intermediate-resistant and resistant isolates, from 4.9% in 1996 to the present rate of 10%, was observed. There was also a distinct rise in the resistance levels of S. pneumoniae against the macrolides. All tested isolates of S. pyogenes were susceptible to penicillin and telithromycin, and only low levels of resistance against telithromycin were found in S. aureus (2.2%, MIC90 of 0.5 mg/L). No telithromycin-resistant isolate of H. influenzae could be detected.

This study demonstrates the rising prevalence of resistance among S. pneumoniae not only to penicillin but also to other antimicrobials. It also shows the value of telithromycin as an attractive option for the empirical treatment of community-acquired RTIs in an era of widespread antibacterial resistance.