Understanding the epidemiology, transmission and pathology of a 21st Century human and animal pathogen, Clostridium difficile

  • Natalie Vardy

Student thesis: Doctoral ThesisDoctor of Philosophy


Clostridium difficile, also known as Clostridioides difficile, is an anaerobic, toxigenic, spore forming Gram-positive bacteria. This opportunistic pathogen is capable of infecting both humans and animals, making it a pathogen of increasing clinical and agricultural significance. Sporulation is intrinsic to the transmission and survival of C. difficile as it enables this anaerobic organism to exist outside of the anaerobic environment in a dormant state. Previous work by Connor et al. (2019) has shown the emergence of a non-sporulating variant (NSV). The NSV is characterised by its inability to undergo sporulation. These NSV were found to have a mutation within the master sporulation regulator, spo0A, which was hypothesised to introduce a premature stop codon into Spo0A, thereby resulting in the sea sporogenous variants. The production of a NSV appears paradoxical; the loss of a vital trait not seemingly desirable to enhance fitness during evolutionary selection. In the current study we report the emergence of the C. difficile NSV in multiple isolates from different ribotypes andnon-cryptic clades. We also observed reversion of the NSV back to a sporulating -variant (SV), and the subsequent reisolation of the NSV from the reverted SV. We identified different mutation sites and types of mutation within spo0Aof the NSV. Further to this, we predicted that some mutations in spo0Acan lead to an alteration of Spo0A structure and therefore function. However we also provide evidence for a loss of sporulation in the NSV independent of spo0Amutation. Finally, we identified multiple metabolic pathways with differential protein expression in the NSV compared to the SV. While the existence of the C. difficile NSV is still somewhat paradoxical, this study provides several theories for its emergence.

Thesis is embargoed until 31 July 2028.
Date of AwardJul 2023
Original languageEnglish
Awarding Institution
  • Queen's University Belfast
SponsorsNorthern Ireland Department for the Economy
SupervisorDerek Fairley (Supervisor), Geoff McMullan (Supervisor) & John McGrath (Supervisor)


  • C. difficile
  • mon-sporulating
  • NSV
  • sporulation
  • spo0A

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