Recherche UV du leader mondial de l’information et de l’analyse

Abstract

An XeBr excilamp having a peak emission at 283 nm, and microwave UV lamps with peak emissions at 253.7 nm that also generate ozone, have been tested for ability to eradicate high populations of microbial vegetative cells and spores (of bacteria and fungi) artificially added to filter surfaces. The study examined the energy required to completely eradicate large populations on filter surfaces. It was found that both the excilamp and microwave UV lamps were effective at killing large populations on surfaces with killing efficiency dependant on the type of organism, and, whether present in its vegetative or spore forms. The main killing factor is UV radiation following short treatment times. It is considered that for longer irradiation periods that are required to facilitate complete destruction of surface microorganisms, ozone and other oxidising species produced by microwave UV lamps would act to enhance microbial destruction.

^{Introduction Microorganisms and their resting stages, such as spores, are abundant in the atmosphere and settle onto surfaces where they can grow and form a dispersed accumulation of cells or simple and complex biofilms depending on the physicochemical environmental conditions. Microorganisms also invade surfaces following contact with humans and other vertebrates and invertebrates, such as flies. Biowarfare is another possible means by which pathogenic microorganisms can be introduced to surfaces and compromise the human living environment. Such pathogenic microorganisms include the causative agent of anthrax, Bacillus anthracis, the spores of which commonly occur in soils. The organism can cause pulmonary, cutaneous and gastrointestinal diseases in animals and humans. Spores of a particularly virulent strain, the Ames strain, were used in anthrax attacks in the USA in 2001 (Wein et al., 2003). Although the minimum infective dose for pulmonary anthrax is not known, the LD50 quoted is 8 × 103–4 × 104 spores (Bartlett et al., 2002). This may not be the case for cutaneous anthrax where small spore numbers in contact with broken skin may be sufficient for disease. Important environments that become contaminated include military vehicles and buildings, and, together with contaminated clothing and equipment used by people, there is a requirement for effective decontamination. Whether bacteria grow and form biofilms or not is irrelevant to possible acquired infection and there is a need to develop robust decontamination systems for surfaces of interest such as hospital floors, walls, kitchen surfaces and other reservoirs of infection (Sharp and Roberts, 2006). Infection control needs to be done for a range of microorganisms that commonly cause disease in humans. Many studies dealing with microbial eradication in aqueous suspension or on surfaces use specific treatment conditions to determine the log reduction of different microbial types and there is little work on the application of UV technologies to the complete eradication of biological entities from accessible and inaccessible environments, natural decay on surfaces and ability to disinfect using UV following long-term presence into the environment. A considered approach to surface disinfection includes the use of UV radiation delivered by arc and microwave, or electrodeless lamp technologies. The aim of this study was to determine the natural decay of microorganisms on natural surfaces and complete eradication of these biological entities from contaminated surfaces using two types of UV lamps. These are excilamps (Sosnin et al., 2006) and electrodeless microwave (MW) UV lamps (Gritsinin et al., 1999, Bergman et al., 2002, Barkhudarov et al., 2003). An excilamp is the collective name given to excimer (rare gas or halogen fill) or an exciplex (rare gas halide fill) lamp that emits UV or vacuum UV (VUV) radiation with a narrow wave band. The excilamp used to affect microbial killing is the XeBr type emitting UV at 283 nm. The MW UV lamps used in this study are low-pressure gas fill lamps containing argon and mercury. Bacterial decay was studied for newly contaminated surfaces (newly prepared films on membrane filters) and for bacterial films allowed to remain in a dry environment for 24 h and 168 h periods representing long-term contamination. This study is part of a larger project to examine degradation of chlorophenolic waste chemicals produced in the paper industry and destruction of microorganisms in waste streams using advanced oxidation processes and utilising UV from various sources.}

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