Antimicrobial activity of the protozoan toxin climacostol and its derivatives

Climacostol is a defense toxin produced by the ciliated protozoan Climacostomum virens and belongs to resorcinolic lipids, a group of compounds that shows antimicrobial, antiparasitic, and cytotoxic activities. In this study we investigate the antimicrobial activity of climacostol and its alkyl and alkynyl derivatives against a panel of bacterial and fungal pathogens. Our results show a good and comparable antimicrobial activity of the three compounds, which have resulted effective against Gram-positive bacteria and Candida with MIC and MBC ranging from 8 to 32 mg L⁻¹, whereas no significant effect against Gram-negative species has been observed. Taken as a whole, the experimental data reported in the current study suggest that differences in the saturation rate of the lateral chain of climacostol are not related to the activity of the molecule. Therefore, it is likely that the general structure of the two moieties, i.e., the di-hydroxy-phenyl group and the alkenyl chains, contributes to the overall antibiotic behaviour.