The anaerobic pathogen Clostridioides difficile has become a major cause of infectious diarrhea in healthcare settings. However, considering that C. difficile spores are highly resistant and considering that pigs and other farm and domestic animals reveal a large reservoir, eradication of C. difficile from our environment seems impossible. Moreover, use of infeed antibiotics in livestock farming increases risk for the development of antibiotic resistance in C. difficile. Thus, the aims of our project are to identify and characterize new compounds active against C. difficile and to evaluate the potential of infeed antibiotics for selection of antibiotic resistance.
As a starting point, we screened selected natural products for their activity against C. difficile and identified three compounds with bactericidal activity against C. difficile at relatively low concentrations when compared to reference antibiotics. For these three compounds and their derivatives minimal inhibitory concentrations were determined for human and porcine C. difficile isolates. Subsequently, C. difficile was exposed to sublethal concentrations of selected compounds and reference antibiotics and protein expression profiles of unstressed and antibiotic-exposed cells were characterized by a comparative gel-free proteomics approach. Finally, sub-lethal concentrations of one compound and a reference antibiotic were administrated to piglets and the composition of the gut microbiota is currently monitored by 16S rRNA gene sequencing and meta-transcriptomic and -proteomic analyses of feces. Thereby, we would like to address the question whether sublethal doses of the natural product or of reference antibiotic select for antibiotic resistance markers in the gastrointestinal tract of the piglets.
By characterizing the mode-of-action of the three natural products our work is expected to help evaluating these products for their use in C. difficile infection therapy. Additionally, a set of meta-data will be derived that putatively will help to clarify the role of infeed antibiotics in the selection process for antibiotic resistance.