Susceptibility of Chlamydia trachomatis to chlorhexidine gluconate gel

To identify topical antimicrobial preparations which may be effective in preventing the transmission of sexually transmitted diseases, we examined the activity of chlorhexidine gluconate (CHG) against Chlamydia trachomatis. Chlamydial elementary bodies were incubated with dilutions of CHG gel for various times from 0 to 120 min. An aliquot of each dilution was further diluted and was inoculated onto McCoy cell monolayers in individual wells in a 96-well microtiter plate. The cultures were incubated for 48 h, and the chlamydial inclusions were stained and counted. CHG gel diluted fourfold (0.0625% CHG) killed C. trachomatis serovar D, and CHG gel diluted eightfold (0.0313% CHG) killed serovar F immediately upon exposure. CHG gel diluted 16-fold (0.0156% CHG) killed serovar D, and CHG gel diluted 32-fold (0.0078% CHG) killed serovar F after 120 min of exposure. Alteration of the pH over the range of from 4 to 8 did not significantly affect its activity. The addition of 10% whole human blood decreased the CHG gel activity at 0 min but had no significant effect after 120 min of exposure. We conclude that CHG gel may be effective topically against C. trachomatis at concentrations that can be used and under conditions that are found in the female genital tract and that further studies of its antimicrobial efficacy and toxicity in vivo are warranted.