Minimum Inhibitory and Minimal Lethal Concentration against <i>Chlamydia trachomatis</i> Dependent on the Time of Addition and the Duration of the Presence of Antibiotics

Abstract

The purpose of this study was to investigate the properties of several antimicrobial agents found to be effective against Chlamydia trachomatis and to verify the eradication therapy schedule. The in vitro activities of two quinolones (sparfloxacin, ofloxacin), of three macrolides (azithromycin, erythromycin, clarithromycin) and of a tetracycline (doxycycline) against C. trachomatis were evaluated by several methods for the determination of the minimum inhibitory concentration (MIC) and minimal lethal concentration (MLC). MLC of azithromycin was only 2 times higher than that of MIC. On the other hand, MLCs of other antibiotics were 4–16 times higher than their respective MICs. When all antimicrobial agents were added to the infected culture at different times, we found that the quinolones even at a concentration of 64 μg/ml could not inhibit the formation of inclusion if they were added after 20 h from the start of infection. The corresponding period for macrolides and doxycycline was 24 h. When the antibiotics were removed at 8 h after the start of the infection, all antibiotics except azithromycin and clarithromycin were needed at a concentration much higher than their MLCs to inhibit the formation of inclusion. We consider macrolides, especially azithromycin, to be an excellent anti-C. trachomatis drug because of its lower MICs and MLCs values which were also closer together.

Analysis of antibiotic resistance markers in Chlamydia trachomatis clinical isolates obtained after ineffective antibiotic therapy

“…Antibiotic therapy is effective, if correct AB dose is calculated with conside- MIC of AB directly depends on the time of AB penetration into the cells (before or after infection). This is confirmed by the results of in vitro experiments: fluoroquinolones in a concentration of 64 µg/ml do not inhibit the formation of chlamydial bodies if they are added 20 h after infection [10]; MIC of macrolides, fluoroquinolones, and tetracyclines drastically increase if these AB are added 8 h after infection [14]. In turn, according to phar- Heterotypical resistance is an additional factor, contributing to AB inefficiency, if its concentration is higher than the minimum tolerated concentration, but lower than MIC.…”

Methodologies and Cell Lines Used for Antimicrobial Susceptibility Testing of Chlamydia spp

“…Additional variables that may influence results of susceptibility testing in Chlamydia, but which have been incompletely studied, include the inoculum size, the interval between the establishment of infection and the administration of an antimicrobial, and the timing of antimicrobial removal (21). We observed no differences in MICs when antimicrobials were added from 0 to 8 h after infection, while the MIC increased steadily after 8 h. Notomi et al reported that the addition of ofloxacin or sparfloxacin even at concentrations up to 64 g/ml could not inhibit the formation of C. trachomatis inclusions when added 20 h after the start of infection (21).…”

Effects of Azithromycin and Rifampin onChlamydia trachomatisInfection In Vitro

“…An experimental setting of this kind, however, is not truly reflective of the situation in vivo for chlamydial infection, since determination of the MIC is done by addition of the antibiotics soon after infection of the cell culture or sometimes simultaneously with infection of the cell culture. Some studies have shown an increase in the MIC when the antibiotic is added up to 24 h after inoculation (41,42). The main disadvantage of these models is the short incubation period of at most 72 h, which is not sufficient to investigate whether the drugs are capable to eradicate chlamydia from the host cells.…”

“…Previous clinical trials revealed high cure rates after treatment of acute, urogenital chlamydial infections with azithromycin (20,21,32,34,40,41,49). Surprisingly, the in vitro inhibitory effect of azithromycin developed relatively slowly compared to the time to the development of the inhibitory effect in the in vivo study, and prolonged incubation was not successful in complete eradication of chlamydial antigens.…”