Susceptibility of Clostridium difficile to 405 nm light and possible mechanisms to enhance sporicidal activity

  • Sian Moorhead

Student thesis: Doctoral Thesis


Clostridium difficile is currently one of the most significant causative agents of healthcare-associatedinfection. The ability of C. difficile to form highly resilient spores has limited the competence of current strategies for environmental decontamination, and advances to reduce environmental contamination and patient infection are urgently sought. The results of this study demonstrate the sporicidal efficacy of 405 nm violet-blue light to achieve up to 5 log₁₀ reductions in C. difficile spores. In comparison, vegetative cells demonstrated an increased susceptibility, requiring a 10-fold lower dose to achieve acomparable level of inactivation.This study progressed to demonstrate enhanced sporicidal efficacy upon combination of chlorinated disinfectants with 405 nm light at both high (up to 225 mWcm⁻²) and low (0.4 mWcm⁻²) irradiances. For decontamination of spores in suspension, a 50% increased spore susceptibility was observed upon exposure to a 33% lower light dose when incombination disinfectants. On clinically-relevant surfaces, up to 100% increased sporereductions were observed upon combination of low irradiance 405 nm light with selecteddisinfectants.Further significant findings of this study include the enhanced susceptibility of spores upon triggering germination, with inactivation achieved using up to 77% less dose. Also established was the critical requirement of oxygen for photo-inactivation of this anaerobic pathogen, thus supporting the mechanism being a result of photoexcitation of naturally-occurring porphyrins inducing ROS production, oxidative damage and ultimately cell death. This study has confirmed the fundamental sporicidal efficacy of 405 nm light and further highlights possible mechanisms to enhance sporicidal activity. 405 nm light has several advantages over current in-house cleaning procedures and novel sporicidal technologies, including its safety for human exposure permitting continuous decontamination of the patient environment, and the work of this thesis supports the potential for sporicidal efficacy to be achieved if utilised as a complementary strategy with standard cleaning regimes.
Date of Award28 Sep 2017
Original languageEnglish
Awarding Institution
  • University Of Strathclyde
SponsorsEPSRC (Engineering and Physical Sciences Research Council)
SupervisorMichelle Maclean (Supervisor) & Scott MacGregor (Supervisor)

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