The spermicide nonoxynol-9 does not inhibit Chlamydia trachomatis in vitro

The antimicrobial effects of the active ingredient, nonoxynol-9, and the base component of a commercially available spermicide were tested in vitro against Chlamydia trachomatis. The infectivity of cell-free elementary bodies was not affected by nonoxynol-9 or the base after incubation for 30, 60, or 180 min in direct contact with serial twofold dilutions of each agent. The spermicide's effect on the in-vitro growth of C. trachomatis was evaluated after exposure of C. trachomatis-infected McCoy cells to serial dilutions of each agent for 2 hr and for 72 hr. A significant cytopathic effect of nonoxynol-9 on the host cell membrane was observed at concentrations of spermicide between 100% and 0.0014%. However, neither agent was effective in inhibiting the intracellular growth of C. trachomatis at concentrations (0.0014-0.0004%) of nonoxynol-9 that produced no evident cytopathic effect on McCoy cells. Thus, nonoxynol-9 was found to be ineffective in inhibiting infectivity or subsequent growth of C. trachomatis.