In vitro susceptibilities of urogenital Chlamydia trachomatis to five antimicrobial agents alone or in combination

Abstract

Objective To test the in vitro acitivity of azithromycin, minocyline, moxifloxacin, doxycycline and rifampicin alone or in combination against three standard strains of urogenital Chlamydia trachomatis,i.e. D-UW-5/Cx, E-UW-5/Cx and G-UW-5/Cx. Methods Three standard strains of C. trachomatis were inoculated into McCoy cells, and used to susceptibility testing after more than 90% McCoy cells were infected.Microdilution method was applied to determine the activity of the 5 antimicrobial agents alone, and checkerboard array to determine that in combination. Results The in vitro minimal inhibitory concentrations (MICs)were 0.25 mg/L for azithromycin, 0.06 mg/L for moxifloxacin, 0.063 - 0.25 mg/L for doxycycline, 0.032 -0.064 mg/L for minocyline, 0.008 mg/L for rifampicin. And, the fractional inhibitory concentration index was constantly 0.75 for the combination of azithromycin with moxifloxacin, doxycycline and rifampicin, 2.5, 2.83and 4 for the combination of minocyline with azithromycin, moxilloxacin and rifampicin, respectively. Conclusions As far as the activity against C. trachomatis is concerned, there is a synergism for the combination of azithromycin with moxifloxacin, doxycycline and rifampicin, but antagonism for the combination of minocyline with azithromycin, moxifloxacin and rifampicin. Key words: Chlamydia trachomatis; Anti-infective agents, urinary; Microbial sensitivity tests; Drug interactions