Activity of grepafloxacin and other fluoroquinones and newer macrolides against recent clinical isolates of Chlamydia pneumoniae.

Chlamydia pneumoniae is a frequent cause of community-acquired respiratory tract infection including pneumonia and bronchitis. Quinolones have attracted interest as potential therapy for community-acquired respiratory tract infections because they are active against a wide range of pathogens including C. pneumoniae and Mycoplasma pneumoniae. The in vitro susceptibilities of C. pneumoniae were determined for grepafloxacin, levofloxacin, moxifloxacin, trovafloxacin, clarithromycin and azithromycin. Isolates of C. pneumoniae tested included two reference strains, TW-183 and CM-1, and 12 recent clinical isolates from adults with community-acquired pneumonia. Susceptibility testing was performed in HEp-2 cells grown in 96-well microtiter plates. The MIC was the lowest antibiotic concentration at which no inclusions were seen. The MBC was the lowest concentration which resulted in no inclusions after passage in antibiotic-free medium. Grepafloxacin was the most active quinolone tested with an MIC50 of 0.125 mg/l, MIC90 and MBC90 of 0.5 mg/l. Grepafloxacin may have a role in the treatment of C. pneumoniae infections, but prospective clinical studies utilizing culture are lacking.