Abstract:

Objective To optimize the concentration of polyethylene glycol （PEG） for the growth of Chlamydia trachomatis （Ct） reference strains D-UW-5/Cx and E-UW-5/Cx, and to evaluate the effects of PEG on the sensitivity of Ct to 4 common antibiotics. Methods After the inoculation of Ct standard strains （D-UW-5/Cx and E-UW-5/Cx） into McCoy cell monolayer, different concentrations of PEG were added into the culture medium followed by centrifugation. After 2 hours of incubation at 37 ℃, the inoculum was removed and a complete culture medium containing 1 ?滋g/mL cycloheximide was added followed by another 48-hour culture. Subsequently, the culture was fixed and subjected to iodine staining for the calculation of Ct inclusions and optimization of PEG for the growth of Ct. Some Ct standard strains were used to infect McCoy cells, with PEG （0.7%, wt/vol） added to the culture medium after inoculation and before centrifugation process, and when the infection rate reached higher than 90%, a microdilution method was utilized to evaluate the minimal inhibitory concentration （MIC） of 4 antibiotics, including azithromycin, minocyline, moxifloxacin and doxycycline. Thirty-one clinical specimens, which had been confirmed to be positive for Ct serovar D or E strain, were inoculated into McCoy cell monolayer for the passage of Ct with or without the presence of 0.7% PEG. Results The optimal concentration of PEG was 0.7% for the growth of Ct, and this concentration of PEG could increase the number of inclusion bodies of Ct serovar E by 3.44 folds, and that of Ct serovar D by 3.56 folds. In vitro, the MICs of the 4 antibiotics were consistent between PEG-treated and untreated Ct reference strains. Moreover, PEG notably increased the quantity of inclusion bodies of Ct serovar E or D from clinical specimens after passages. Conclusions PEG （0.7%） can enhance the growth of Ct serovar D and E, but has no obvious influence on antimicrobial susceptibility of Ct.

Key words: Susceptibility test