Decraene, V.; (2008) Light-activated antimicrobial coatings for reducing microbial contamination of surfaces. Doctoral thesis , University of London.

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Abstract

Environmental surface contamination can contribute to cross-infection within hospitals by acting as a reservoir from which personnel and patients can soil their hands. It is important, therefore, to develop effective means of reducing the microbial load on such surfaces. One possible approach involves the use of photosensitisers, compounds which generate antimicrobial moieties (e.g. singlet oxygen), when irradiated with an appropriate light source. The overall aim of this study was to develop a coating containing photosensitisers that is able to kill microbes when irradiated with light generated by the type of lamp recommended for use in hospitals in the United Kingdom i.e. a 28 W General Electric fluorescent lamp. After comparing the absorption spectra of candidate compounds with the emission spectrum of the light source, the following photosensitisers were selected for study: Toluidine Blue O (TBO), Methylene Blue (MB), Methylene Violet (MV), Rose Bengal (RB), and Erythrosine B (ErB). The singlet oxygen ('02) producing ability of the selected compounds was then tested using the uric acid assay. All photosensitisers had comparable rates of lOj production but both ErB and RB became photobleached over time. Based on these results, TBO, MB and MV were selected for further study and lethal photosensitisation experiments were carried out using aqueous suspensions of Staphylococcus aureus, Escherichia coli, Candida albicans and Bacteriophage OX 174. All three photosensitisers produced significant kills against these four organisms but, while 2 hours of irradiation was sufficient for bacteria, longer (6 hour) irradiation was necessary to achieve substantial kills of the bacteriophage and yeast. These photosensitisers were then incorporated into cellulose acetate coatings, and the antimicrobial activity of these coatings was investigated. MV was found to be inactive when immobilized in the polymer and was therefore replaced by RB. The optimal coating of those tested contained a combination of 25 uM TBO and 25 uM RB. This coating was able to generate appreciable kills of a range of different microbes both when aliquoted on to the coating as a suspension and when sprayed on using a nebuliser. Significant kills were also achieved in the presence of horse serum and saliva and following prolonged irradiation of the coatings. A study of the environmental contamination present in a dental clinic was carried out using settle plates and revealed that both the number and variety of bacteria were significantly greater on days when clinics were held compared to days when there was no clinical activity. The most frequently encountered species were P. acnes, M. 2 2 luteus, and S. epidermidis and the mean total microbial load was 21.9 x 1(T cfu/m7h. The final stage of the project involved testing the activity of the TBO/RB coatings in this clinical setting. When compared to control (photosensitiser-free) coatings, the TBO/RB coatings achieved reduced counts on 12 out of the 15 days, with median reductions of 63.8 % and 81.8 % for aerobic and anaerobic bacteria respectively. Overall, these coatings show potential as a renewable, self-disinfecting surface and may have a range of applications in the hospital environment.

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