In vitro activity of quinupristin/dalfopristin (Synercid, RP 59500) against Legionella spp.

The activities of quinupristin/dalfopristin (Synercid), erythromycin and azithromycin against 22 Legionella spp. isolates were measured by a microbroth dilution method. The MICs that inhibited 90% of strains tested were 0.5, 0.35, and 0.5 mu g/mL for quinupristin/dalfopristin, erythromycin, and azithromycin, respectively. Quinupristin/dalfopristin was only partially active against intracellular L. pneumophila at high (2 mu g/mL), but not low (1 mu g/mL) concentration. Activity of the drug in a guinea pig model of Legionnaires' disease could not be accurately determined because of drug toxicity for the guinea pig, although there was evidence that the drug has in vivo activity. (C) 2000 Elsevier Science Inc. All rights reserved.