Inactivation of Clostridium difficile spores in the healthcare environment using hydrogen peroxide vapour
thesisposted on 11.06.2013, 13:37 authored by Claire M. Shaw
Healthcare-acquired infections (HAIs) cost the National Health Service (NHS) in England in excess of £1 billion per year. One of the main HAIs is caused by the endospore-forming bacterium Clostridium difficile. The most common cause of healthcare-acquired diarrhoea in the developed world, C. difficile was responsible for around 850 deaths in England and Wales in 2011. To help reduce the spread of the HAI-causing bacteria, terminal disinfection of isolation rooms and wards using hydrogen peroxide vapour is actively promoted. The key advantages of hydrogen peroxide vapour are its high oxidation potential which has been reported to inactivate bacteria, fungi and spores. An additional advantage of hydrogen peroxide vapour is that it is relatively environmentally friendly, breaking down into oxygen and water. Investigation into bacterial inactivation kinetics was undertaken at controlled, steady concentrations of hydrogen peroxide vapour in the range of 10 ppm to 90 ppm. An exposure chamber was designed whereby the bacterial spores could be exposed to constant concentrations of hydrogen peroxide for various exposure times. Bacterial spores (1-log10 to 8-log10 cfu) were filter deposited onto membranes to achieve an even layer for consistent exposure of the hydrogen peroxide vapour to the spores. Bacillus subtilis is often used for method development in bacterial studies; advantages are it has been shown to be highly resistant to hydrogen peroxide vapour and is not a human pathogen. Following the method development, different strains of C. difficile (ribotypes 014, 027, 103 and 220) were exposed to identify differences in resistance. Inactivation models (Chick-Watson, Series-Event, Weibull and Baranyi) were used to fit the data generated using the environmental chamber. Decimal reduction values (D-values) were calculated from the models for comparative studies regarding the inactivation achieved for the different bacteria and different hydrogen peroxide concentrations. The findings from this thesis revealed the Weibull model provides the best fit for most of the data. An initial shoulder period was identified for B. subtilis which was absent for C. difficile inactivation by hydrogen peroxide vapour; B. subtilis is therefore more resistant to hydrogen peroxide disinfection than C. difficile. Typical D-values for B. subtilis and C. difficile when exposed to hydrogen peroxide vapour at a concentration of 90 ppm were 140 and 1 min, respectively. C. difficile inactivation data were used to develop a model to estimate the log reduction that could be achieved during an inactivation cycle based on the concentration-time integral ( ). This model could be used to estimate the log reduction of commercially available hydrogen peroxide decontamination systems; these release a fixed amount of hydrogen peroxide into the room resulting in a peak concentration before decomposition to oxygen and water. Releasing the hydrogen peroxide into the room in this manner results in spatial and temporal variation; this could result in differences in bacterial inactivation in different areas within the room. Using the aforementioned regression model, the inactivation achieved at all locations within the room could be predicted, which could be used to optimise the current hydrogen peroxide decontamination cycles.
This work was supported by the Engineering and Physical Sciences Research Council (EPSRC).
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