The natural product chlorotonil A preserves colonization resistance and prevents relapsing Clostridioides difficile infection

Clostridioides difficile infections (CDIs) remain a healthcare problem due to high rates of relapsing/recurrent CDIs (rCDIs). Breakdown of colonization resistance promoted by broad-spectrum antibiotics and the persistence of spores contribute to rCDI. Here, we demonstrate antimicrobial activity of the natural product class of chlorotonils against C. difficile. In contrast to vancomycin, chlorotonil A (ChA) efficiently inhibits disease and prevents rCDI in mice. Notably, ChA affects the murine and porcine microbiota to a lesser extent than vancomycin, largely preserving microbiota composition and minimally impacting the intestinal metabolome. Correspondingly, ChA treatment does not break colonization resistance against C. difficile and is linked to faster recovery of the microbiota after CDI. Additionally, ChA accumulates in the spore and inhibits outgrowth of C. difficile spores, thus potentially contributing to lower rates of rCDI. We conclude that chlorotonils have unique antimicrobial properties targeting critical steps in the infection cycle of C. difficile.

Functionalization of Chlorotonils: Dehalogenil as Promising Lead Compound for In Vivo Application

The natural product chlorotonil displays high potency against multidrug-resistant Gram-positive bacteria and Plasmodium falciparum. Yet, its scaffold is characterized by low solubility and oral bioavailability, but progress was recently made to enhance these properties. Applying late-stage functionalization, we aimed to further optimize the molecule. Previously unknown reactions including a sulfur-mediated dehalogenation were revealed. Dehalogenil, the product of this reaction, was identified as the most promising compound so far, as this new derivative displayed improved solubility and in vivo efficacy while retaining excellent antimicrobial activity. We confirmed superb activity against multidrug-resistant clinical isolates of Staphylococcus aureus and Enterococcus spp. and mature transmission stages of Plasmodium falciparum. We also demonstrated favorable in vivo toxicity, pharmacokinetics and efficacy in infection models with S. aureus. Taken together, these results identify dehalogenil as an advanced lead molecule.

Natural products chlorotonils exert a complex antibacterial mechanism and address multiple targets

Antimicrobial resistance is a threat to human health rendering current first-line antibiotics ineffective. New agents overcoming resistance mechanisms are urgently needed to guarantee successful treatment of human disease in the future. Chlorotonils, a natural product class with yet unknown mode of action, were shown to have broad-spectrum activity against multi-resistant Gram-positive bacteria and the malaria parasite Plasmodium falciparum, with promising activity and safety in murine infection models. Here, we report that chlorotonils can target the cell membrane, cell wall, and protein biosynthesis. They can be characterized by a rapid onset of action via interference with ion homeostasis leading to membrane depolarization, however, without inducing severe barrier failure or cellular lysis. Further characterization confirmed binding of chlorotonils to bacterial membrane lipids eventually leading to uncontrolled potassium transport. Additionally, we identified functional inhibition of the peptidoglycan biosynthesis protein YbjG and methionine aminopeptidase MetAP as secondary targets of chlorotonils.