title: Impact on toxin production and cell morphology in Clostridium difficile by ridinilazole (SMT19969), a novel treatment for C. difficile infection.
abstract: OBJECTIVE
  Ridinilazole (SMT19969) is a narrow-spectrum, non-absorbable antimicrobial with activity against Clostridium difficile undergoing clinical trials. The purpose of this study was to assess the pharmacological activity of ridinilazole and assess the effects on cell morphology.
  
  
  METHODS
  Antibiotic killing curves were performed using the epidemic C. difficile ribotype 027 strain, R20291, using supra-MIC (4× and 40×) and sub-MIC (0.125×, 0.25× and 0.5×) concentrations of ridinilazole. Following exposure, C. difficile cells were collected for cfu counts, toxin A and B production, and morphological changes using scanning electron and fluorescence microscopy. Human intestinal cells (Caco-2) were co-incubated with ridinilazole-treated C. difficile growth medium to determine the effects on host inflammatory response (IL-8).
  
  
  RESULTS
  Treatment at supra-MIC concentrations (4× and 40× MIC) of ridinilazole resulted in a significant reduction in vegetative cells over 72 h (4 log difference, P < 0.01) compared with controls without inducing spore formation. These results correlated with a 75% decrease in toxin A production (P < 0.05) and a 96% decrease in toxin B production (P < 0.05). At sub-MIC levels (0.5× MIC), toxin A production was reduced by 91% (P < 0.01) and toxin B production was reduced by 100% (P < 0.001), which resulted in a 74% reduction in IL-8 release compared with controls (P < 0.05). Sub-MIC (0.5×)-treated cells formed filamentous structures ∼10-fold longer than control cells. Following fluorescence labelling, the cell septum was not forming in sub-MIC-treated cells, yet the DNA was dividing.
  
  
  CONCLUSIONS
  Ridinilazole had robust killing effects on C. difficile that significantly reduced toxin production and attenuated the inflammatory response. Ridinilazole also elicited significant cell division effects suggesting a potential mechanism of action.
authors.affiliation: University of Houston College of Pharmacy, 1441 Moursund Street, Houston, TX 77030, USA.
authors.forename: Eugénie
authors.initials: E
authors.lastname: Bassères
authors.affiliation: University of Houston College of Pharmacy, 1441 Moursund Street, Houston, TX 77030, USA.
authors.forename: Bradley T
authors.initials: BT
authors.lastname: Endres
authors.affiliation: University of Houston College of Pharmacy, 1441 Moursund Street, Houston, TX 77030, USA.
authors.forename: Mohammed
authors.initials: M
authors.lastname: Khaleduzzaman
authors.affiliation: University of Houston College of Pharmacy, 1441 Moursund Street, Houston, TX 77030, USA.
authors.forename: Faranak
authors.initials: F
authors.lastname: Miraftabi
authors.affiliation: University of Houston College of Pharmacy, 1441 Moursund Street, Houston, TX 77030, USA.
authors.forename: M Jahangir
authors.initials: MJ
authors.lastname: Alam
authors.affiliation: Summit Therapeutics, 85b Park Drive, Milton Park, Abingdon, Oxfordshire OX14 4RY, UK.
authors.forename: Richard J
authors.initials: RJ
authors.lastname: Vickers
authors.affiliation: University of Houston College of Pharmacy, 1441 Moursund Street, Houston, TX 77030, USA kgarey@central.uh.edu.
authors.forename: Kevin W
authors.initials: KW
authors.lastname: Garey
mesh_terms: D000900:Anti-Bacterial Agents / Q000494:pharmacology*; D001427:Bacterial Toxins / Q000378:metabolism*; D001562:Benzimidazoles / Q000494:pharmacology*; D018938:Caco-2 Cells; D016360:Clostridioides difficile / Q000166:cytology / Q000187:drug effects* / Q000378:metabolism; D016207:Cytokines / Q000378:metabolism; D004847:Epithelial Cells / Q000382:microbiology; D006801:Humans; D008826:Microbial Sensitivity Tests; D050296:Microbial Viability / Q000187:drug effects; D008855:Microscopy, Electron, Scanning; D011725:Pyridines / Q000494:pharmacology*
chemical_list: D000900:Anti-Bacterial Agents; D001427:Bacterial Toxins; D001562:Benzimidazoles; D016207:Cytokines; D011725:Pyridines; C000601750:ridinilazole