Pal, Rusha2023-01-132023-01-132023-01-12vt_gsexam:35974http://hdl.handle.net/10919/113162Investigating novel treatment approaches to combat Clostridioides difficile Rusha Pal ABSTRACT Clostridioides difficile is the leading cause of antibiotic-induced diarrhea and colitis in hospitals and communities worldwide. The enteric pathogen, classified to be an "urgent threat" by the United States Center for Disease Control and Prevention (CDC), capitalizes on disrupted intestinal microbiome to establish infection with disease symptoms ranging from mild diarrhea to potentially fatal conditions. Disruption of the intestinal microbiome, caused mostly by antibiotic use, enables C. difficile to colonize and proliferate within the host. Paradoxically, antibiotics are used to treat C. difficile infection. These antibiotics decimate the gut microbial community further, thus priming the gastrointestinal tract to become more prone to recurrence of infection. To tackle this clinical setback, we utilized a combination of traditional and non-traditional drug discovery approaches and identified chemical entities and targeted treatment options effective against this toxin-producing intestinal pathogen. Herein, we exploited the strategy of high-throughput screening to identify leads that harbor anticlostridial activity. Our primary phenotypic screen of FDA-approved drugs and natural product libraries led to the identification of novel molecules that were further characterized for their anticlostridial efficacy both in vitro and in vivo. The most potent scaffolds identified were those of mitomycin C, mithramycin A, aureomycin, NP-003875, NAT13-338148, NAT18-355531, and NAT18-355768. Of these, mithramycin A, aureomycin, and NP-003875 were also found to harbor anti-virulence properties as they inhibited toxin production by the pathogen. Furthermore, natural product NP-003875 could confer protection to 100% of the infected mice from clinical manifestations of the disease in a primary infection model of C. difficile. Our final approach has been to develop targeted therapeutics called peptide nucleic acids (PNAs). PNAs are antisense agents capable of inhibiting gene expression in bacteria. In this study, antisense inhibition of the RNA polymerase  subunit gene (rpoA) of C. difficile was found to be bactericidal for the pathogen and could also inhibit the expression of its virulence factors. Additionally, antisense inhibition of the C. difficile rpoA gene was found to be non-deleterious for the tested commensal microflora strains. Given their intriguing anticlostridial properties, it can be concluded that our research opened exciting possibilities that can be further evaluated to uncover new treatments for CDI.ETDenIn CopyrightClostridioides difficiledrug discoveryrecurrencedrug repurposinghigh-throughput screeningpeptide nucleic acidDissertation