Sporicidal efficacy of the combined use of 405nm light and disinfectants for inactivation of Clostridium difficile on clinically relevant surfaces.

Research output: Contribution to conferencePosterpeer-review


The ability of Clostridium difficile to form highly infectious and resilient spores which can survive in the environment for prolonged periods causes major contamination problems. Antimicrobial 405 nm light is capable of inactivating a wide range of organisms, including endospore-forming bacteria, and is being developed for environmental decontamination within hospitals. Currently, there are several drawbacks associated with the chlorinated disinfectants recommended for surface decontamination, including their corrosive nature and the release of irritating vapours affecting healthcare workers. This study aims to establish whether spore susceptibility to low concentration chlorinated disinfectants can be enhanced when used in conjunction with 405 nm light.Spores were spot inoculated and dried onto PVC, vinyl flooring and stainless steel. Samples were then simultaneously exposed to disinfectants (0.0001% Tristel, 0.001% Actichlor and 0.1% sodium hypochlorite (NaOCl)) and 405 nm light at an irradiance of 225 mWcm-2. Control samples were exposed to 405 nm light alone, and disinfectants alone, to establish the sporicidal activity of each agent, and to demonstrate the synergistic effect when combined. Results showed that spores exposed to 405 nm light alone were reduced by 1-2 log10 on all surfaces after a dose of 2.4 kJcm-2. On PVC, complete inactivation was achieved following a dose of 0.8 kJcm-2in the presence of NaOCl, and >2 log10 reduction was achieved following exposure to 0.8 kJcm-2and 1.6 kJcm-2 in combination with Actichlor and Tristel, respectively. Sporicidal activity was significantly enhanced in the presence of all three disinfectants on vinyl, with a 2.5-3 log10 reduction achieved following exposure to a dose of 1.6 kJcm-2 in the presence of both Actichlor and NaOCl. However on stainless steel, spores demonstrated higher resilience to the combined oxidative effects of 405 nm light and disinfectants, with a dose of 2.4 kJcm-2required to achieve a 1.5-2 log10 reduction for all 3 disinfectants.In conclusion, the sporicidal efficacy of commonly used chlorinated hospital disinfectants can be enhanced on a range of clinically relevant surfaces when used alongside 405 nm light. However, the extent of the enhanced sporicidal activity is dependent on the disinfectant and the surface it is applied to. This has the potential to lead to a considerable reduction in exposure time and concentrations of disinfectant required to eliminate C. difficile spores. Further research may lead to potential use of 405 nm light decontamination in combination with selected hospital disinfectants to enhance C. difficile cleaning and infection control procedures.
Original languageEnglish
Publication statusPublished - 23 Nov 2015
EventAction on Infection conference - Glasgow, United Kingdom
Duration: 21 Nov 201523 Nov 2015


ConferenceAction on Infection conference
Country/TerritoryUnited Kingdom


  • Clostridium difficile
  • 405nm light
  • disinfectants
  • sporicidal


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