Kaempferol inhibits Chlamydia psittaci proliferation by blocking lipid transport and RB-EB differentiation.

Chlamydia psittaci is an obligate intracellular pathogen that poses a significant threat to both human and animal health. The current therapeutic strategies are limited by the emergence of potential drug resistance, underscoring the urgent need for novel anti-chlamydial agents. In this study, we evaluated the anti-chlamydial activity of kaempferol, a natural occurring flavonoid. Potential targets of kaempferol and C. psittaci infection-related targets were identified through in silico screening. In cellular assays using both HeLa and THP-1 cells, kaempferol treatment significantly inhibits the intracellular growth of C. psittaci in a dose-dependent manner, while showing no host cell cytotoxicity at effective concentrations. Based on prior in silico virtual screening and our group's systematic evaluation of the anti-chlamydial activity of flavonoids, kaempferol (40 μM) was selected as the target compound for this study due to its potent antimicrobial effects and its potential to modulate key host-pathogen interaction pathways. Mechanistic investigations revealed that kaempferol interferes with the trafficking of host-derived lipid to the bacterial inclusion, thereby depriving the pathogen of essential nutrients. Moreover, kaempferol treatment severely disrupted the normal differentiation of reticulate bodies (RBs) into infectious elementary bodies (EBs), resulting in an aberrant developmental cycle and a reduction in the production of new infectious progeny. This study demonstrates that kaempferol exerts anti-chlamydial activity by targeting two key processes of C. psittaci infection: lipid trafficking to inclusions and RB-EB conversion. These results highlight kaempferol as a promising lead compound for developing new therapeutic approaches against C. psittaci infections.