Limonene and its metabolite perillyl alcohol inhibit Chlamydia trachomatis growth by altering host isoprenoid metabolism

Abstract The obligate intracellular bacterium Chlamydia trachomatis is the most common bacterial sexually transmitted infection globally, with approximately 131 million new cases each year. It contributes to widespread reproductive health issues, including infertility and chronic pelvic pain. The unique cell morphology and biphasic life cycle pose challenges to their effective eradication. Guided by the identification of essential oils (EOs) capable of suppressing C. trachomatis intracellular growth, this study evaluated the antichlamydial properties of the monoterpene limonene and its metabolites perillyl alcohol and perilic acid. The antichlamydial activity was assessed through qPCR-based quantification of bacterial genome copy numbers and immunofluorescence staining of chlamydial inclusions to monitor bacterial growth and infectious progeny production. Elementary body membrane integrity was assessed with viability PCR. Citrus limon essential oil exhibited dose-dependent inhibition of C. trachomatis growth, decreasing infectious progeny by over 90%. Pinus sylvestris EO displayed consistent but non-dose-dependent effects. Limonene, a major constituent of the EOs, exhibited significant suppression of chlamydial growth and progeny production, particularly for its R-enantiomer. While viability-PCR data indicated that the EOs and limonene affected EB membrane permeability, EB infectivity was not affected by the treatments. Perillyl alcohol suppressed chlamydial growth at a lower concentration (100 µg mL −1 ) than the parent compound limonene. The antichlamydial activity of both limonene and perillyl alcohol was suppressed when infected cultures were supplemented with farnesyl or geranylgeranyl, indicating that the antichlamydial mechanism of the two monoterpenes involves competitive inhibition of protein prenylation. Hence, targeting host protein prenylation may be an effective antichlamydial strategy. Graphical Abstract