In-vitro activity of RP 59500, a new synergic antibacterial agent, against Legionella spp.

The in-vitro activity of RP 59500, a new semisynthetic injectable streptogramin, was compared with that of erythromycin, rifampicin and ciprofloxacin against 189 Legionella spp. Rifampicin was the most active agent tested. RP 59500 was found to be more active than erythromycin against most strains, but less active than ciprofloxacin. Legionella pneumophila serogroups 1, 3, 4, 5 and 6 were more susceptible to RP 59500 than were L. pneumophila serogroups 2, 7, and 8. Legionella micdadei was the least susceptible species to RP 59500 and erythromycin. RP 59500 was similar in activity against isolates obtained from both patients and environmental sources. This activity was generally better than that of erythromycin.