Antimicrobial activity of ten macrolide, lincosamine and streptogramin drugs tested against Legionella species.

RP59500, a semisynthetic pristinamycin combination, and 14 other antimicrobial agents were tested against 108 Legionella strains. Of the ten macrolide, lincosamine and streptogramin agents tested, the new streptogramin RP59500 ranked seventh in order of activity against Legionella pneumophila on the basis of MIC90 results as follows: clarithromycin = 14-OH clarithromycin (MIC90 0.12 mg/l) > roxithromycin > erythromycin = tylosin = virginiamycin > RP59500 (MIC90 1 mg/l) = azithromycin > dirithromycin > clindamycin (MIC90 8 mg/l). Of all 14 drugs tested in this study, rifampicin was the most potent with an MIC90 of 0.008 mg/l. In this retrospective study of Legionella strains (1981-1990 isolates), we observed no trend toward resistance to the agents investigated.