Inactivation of clinically relevant pathogens by photocatalytic coatings

Novel disinfection methods are being sought to provide additional means of protection in a number of areas where disease outbreaks could lead to illness or fatalities. For example, the risk of contamination arising from contact with surfaces and medical devices has received much attention due to the rise in incidence of healthcare acquired infections. It is possible that reducing bio-burden on these sites may supplement the disinfection protocols currently in place and help reduce risk of infection. Photocatalytic surfaces offer promise as innovative and cost-effective biocidal engineering solutions which address these specific problems whilst maintaining stringent health and safety controls.A method was developed to assess the disinfection efficiency of photocatalytic surfaces allowing a) determination of pathogen viability as a function of treatment time; b) assessment of the surface for viable surface bound organisms following disinfection; c) measurement of the re-growth potential of inactivated organisms. This method was used to demonstrate the inactivation of extended-spectrum beta-lactamase Escherichia coli, methicillin resistant Staphylococcus aureus, Pseudomonas aeruginosa and Clostridium difficile spores using immobilised films of commercial titania nanoparticles. 99.9% reduction in viability (a 3-log kill) was observed for all bacterial cells within 80 minutes of photocatalytic treatment. Complete surface inactivation was demonstrated and bacterial re-growth following photocatalytic treatment was not observed. Greater than 99% inactivation (2.6 log reduction) was observed when the photocatalytic surfaces were challenged with Clostridium difficile spores.The efficacy of photocatalytic disinfection to inactivate Staphyloccocus epidermidis cells within a biofilm was also demonstrated, with 3 hours treatment rendering 96.5% ± 6 of the biofilm cells on the TiO2 coated substrate non-viable. Disinfection of cells throughout the 3-4 m thick biofilm was observed.