Comparative in vitro susceptibility of Ureaplasma urealyticum and Mycoplasma hominis to macrolides, tetracyclines, 4-quinolones, chloramphenicol, gentamicin, and clindamycin

The in vitro activity of the macrolides, erythromycin, roxythromycin, clarithromycin and azithromycin, the quinolones, ciprofloxacin, ofloxacin and fleroxacin and of tetracycline, doxycycline, chloramphenicol, gentamicin and clindamycin against 50-95 strains of Ureaplasma urealyticum and 20-54 strains of Mycoplasma hominis was determined. Doxycycline (MIC₅₀ 0.125-0.25 μg/ml) and chloramphenicol (MIC₅₀ 4 μg/ml) were very active against both mycoplasmas. Clindamycin was highly active only against M. hominis (MIC₉₀ 0.03 μg/ml) but inactive against U. urealyticum. Clarithromycin (MIC₉₀ 0.25 μg/ml) was the most active macrolide against Ureaplasma urealyticum. The quinolones had a moderate activity against M. hominis (MIC₉₀ 2 μg/ml) but only a poor activity against U. urealyticum (MIC₉₀ 4-8 μg/ml). Mycoplasma hominis showed significant resistance to tetracyclines (13% for doxycycline, 16% for tetracycline).