Bactericidal efficiency of UV-active TiO2 thin films on adhesion and viability of food-borne bacteria

Abstract

Biofilms, containing pathogenic bacteria, represent a recurrent economic and safety problem in food industries, due to their high resistance to cleaning and sanitizing procedures. The development of photoactive surfaces with bactericidal property could facilitate the elimination of such microbial biofilms. One solution may be to deposit a photocatalyst top-layer (TiO 2 ) on conventional materials used in food plants. Our aim is to study the photocatalytic activity of such layers on the adhesion and viability of different bacteria present on food plants, especially in pork meat factory: Listeria monocytogenes, Yersinia enterocolitica and Pseudomonas fragi. Glass substrates were coated with TiO 2 thin films by radio-frequency magnetron sputtering under various deposition conditions (deposition temperature T, oxygen partial pressure P O2 ). The characterization of the TiO 2 thin layers was performed using spectrophotometry, scanning electron microscopy and X-ray diffraction analysis. And photocatalytic activity under UVA illumination (365 nm) has been checked for all samples. Bactericidal activity has been demonstrated on the bacteria tested by enumeration of the adherent cells and in situ fluorescent labeling after three hours of contact with the thin film and a subsequent UVA illumination. Adherent bacteria with damaged bacterial cell wall were observed using a scanning electron microscopy; this can be associated with presence of oxidative stress due to the photocatalytic activity of the TiO 2 thin layer. The selected TiO 2 coating presents a photocatalytic activity leading to an oxidative stress. This activity provides bactericidal properties against different strains from the meat industry. This thin layer could be optimized by modifying anionic composition (band-gap reduction) during coating in order to be active under solar light so it could be used to fight against biofilms.