In vitro activity of azithromycin and erythromycin against organisms associated with bacterial vaginosis and chancroid.

The in vitro activity of the new macrolide azithromycin and erythromycin against Haemophilus ducreyi, Gardnerella vaginalis, Bacteroides spp. and Mobiluncus spp. was compared. Gardnerella vaginalis, Mobiluncus spp. and Haemophilus ducreyi were highly susceptible to both agents but azithromycin was more effective overall against all three groups of organisms. The activity of both antibiotics against Bacteroides spp. varied greatly, but azithromycin was again more active. Collectively, 62% of all Bacteroides strains were susceptible to erythromycin (MIC 1 mg/1) and 74% were susceptible to azithromycin.