Comparative In Vitro Activities of Four Macrolides at Two pH Values Against Gram-negative Anaerobic Rods other than theBacteroides fragilis Group

At this time in the USA there are no antimicrobials with specific indications for oral infections, and many of those currently used have limited efficacy against oral anaerobic strains. We tested the activity of azithromycin against a broad range of anaerobic oral pathogens and, at pH 8, found it to be effective against 98% of strains, including all fusobacteria and β-lactamase-producing strains of Prevotella spp. All strains of Eikenella corrodens were also susceptible to azithromycin but resistant to erythromycin, clindamycin, metronidazole and cefalexin. Other comparator agents were penicillin, amoxicillin/clavulanic acid, tetracycline, levofloxacin and ciprofloxacin. Minimum inhibitory concentrations obtained on agar adjusted to pH 8 were generally one dilution lower than those obtained on agar at pH 7.