In vitro inactivation of Chlamydia trachomatis by fatty acids and monoglycerides

Abstract

The antichlamydial effects of several fatty acids and monoglycerides were studied by incubating Chlamydia trachomatis bacteria with equal volumes of lipid solutions for 10 min and measuring the reduction in infectivity titer compared with that in a control solution without lipid. Caprylic acid (8:0), monocaprylin (8:0), monolaurin (12:0), myristic acid (14:0), palmitoleic acid (16:1), monopalmitolein (16:1), oleic acid (18:1), and monoolein (18:1) at concentrations of 20 mM (final concentration, 10 mM) had negligible effects on C. trachomatis. In contrast, lauric acid (12:0), capric acid (10:0), and monocaprin (10:0) caused a greater than 10,000-fold (>4-log10) reduction in the infectivity titer. When the fatty acids and monoglycerides were further compared at lower concentrations and with shorter exposure times, lauric acid was more active than capric acid and monocaprin was the most active, causing a greater than 100, 000-fold (>5-log10) inactivation of C. trachomatis at a concentration of 5 mM for 5 min. The high levels of activity of capric and lauric acids and particularly that of monocaprin are notable and suggest that these lipids have specific antichlamydial effects. The mode of action of monocaprin was further studied by removal of the lipid by centrifugation before inoculation of Chlamydia onto host cells and by electron microscopy. The results indicate that the bacteria are killed by the lipid, possibly by disrupting the membrane(s) of the elementary bodies. A 50% effective concentration of 30 microgram/ml was found by incubation of Chlamydia with monocaprin for 2 h. The rapid inactivation of large numbers of C. trachomatis organisms by monocaprin suggests that it may be useful as a microbicidal agent for the prevention of the sexual transmission of C. trachomatis.

FIG. 1

Inactivation of C. trachomatis by incubation with equal volumes of 20 mM fatty acids and monoglycerides for 10 min at 37°C. The bars represent the levels of reduction of the log₁₀ numbers of IFU. The levels of inactivation by capric acid and monocaprin (10:0) and by lauric acid (12:0) are greater than those indicated by the bars (>4 log₁₀). Two percent ethanol had no effect on the infectivity titer.

FIG. 2

Electron micrographs of negatively stained EBs of C. trachomatis. The EBs were untreated (A) and treated with 10 mM monocaprin for 1 min (B), 5 min (C), and 10 min (D). After treatment for 10 min, the EBs appear deformed and shrunken or partially disrupted (D, inset). Bars, 1 μm.