Comparison of Antimicrobial Susceptibility Testing Methodologies for Chlamydia Trachomatis

Objective To compare three methods for antimicrobial susceptibility testing on C.trachomatis.Methods McCoy cells were cultured in 96-well plates and 24-well plates with RPMI1640 medium supplemented with 10% calf serum.When the cells came to confluency,the suspension of C.trachomatis in SPG was inoculated onto the monolayers of McCoy cells.After centrifugation,the supernatant was replaced with maintenance medium containing a serially twofold diluted antimicrobial agent.After incubation at 35℃ for 48~72h,the cultures were subjected to iodine staining,immunofluorescence staining or RT-PCR for the examination of in vitro susceptibility of six antibiotics,including erythromycin,azithromycin,clarithromycin,ofloxacin,doxycycline and tetracycline,against two reference strains of C.trachomatis,E and L3.Results For all antibiotics tested,MICs resulted from RT-PCR were consistently higher than those from other two methods,and the increase in MICs ranged from 1～8 folds.The difference was 1～2 folds between iodine staining and immunofluorescence staining.Conclusion For the detection of antimicrobial susceptibility testing of C.trachomatis,compared with the gold standard method,RT-PCR is more objective,while iodine staining is relatively easy to carry out.