Susceptibility of Ureaplasma urealyticum to tetracycline, doxycycline, erythromycin, roxithromycin, clarithromycin, azithromycin, levofloxacin and moxifloxacin

The in vitro activity of tetracycline, doxycycline, erythromycin, roxithromycin, clarithromycin, azithromycin, levofloxacin and moxifloxacin was tested against 63 clinical isolates of Ureaplasma urealyticum. The minimal inhibitory concentrations (MICs) and the minimal bactericidal concentrations (MBCs) were determined by the broth microdilution method in A7 medium. The MIC₅₀ and MIC₉₀ of the tested agents after 24 h of incubation were as follows: tetracycline, 0.5 and 2.0 mg/ml; doxycycline, 0.125 and 0.25 mg/ml; erythromycin, 2.0 and 8.0 μg/ml; roxithromycin, 2.0 and 4.0 μg/ml; clarithromycin, 0.25 and 1.0 μg/ml; azithromycin, 2.0 and 4.0 μg/ml; levofloxacin, 1.0 and 2.0 μg/ml; and moxifloxacin, 0.5 and 0.5 μg/ml, respectively. The MIC values after 24 h and 48 h incubation differed by no more than one dilution for all the agents with the exception of doxycycline (two dilution difference for MIC₉₀). Overall, moxifloxacin was the most active agent in vitro against U. urealyticum, with the narrowest difference between MIC and MBC values, followed closely by levofloxacin. Clarithromycin was the most active macrolide.