Aiken, Z.A.; (2012) Measuring the susceptibility and adhesion of microorganisms to light-activated antimicrobial surfaces. Doctoral thesis , UCL (University College London).

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Abstract

The prevention of healthcare‐associated infections (HCAIs) is a major challenge currently being faced by hospitals in both the UK and worldwide. The hospital environment acts as a reservoir for nosocomial organisms contributing towards the transmission of bacteria and thus the colonisation and infection rates of the patient population. Therefore, it is desirable to implement measures to decrease the microbial load within the hospital environment as a whole and particularly on frequently touched surfaces. Antimicrobial coatings could be applied to these surfaces, and used as an adjunct to other infection control policies to reduce the incidence of HCAIs. Novel nitrogen‐doped, sulfur‐doped and silver‐coated titanium dioxide photocatalytic thin films were generated by sol‐gel or chemical vapour deposition. The materials exhibited antibacterial properties after exposure to a white light commonly used in UK hospitals. However, it was difficult to synthesise reproducible thin films using the CVD method of deposition. An additional antibacterial material was generated with the potential to be used in endotracheal tubes to reduce the incidence of HCAIs such as ventilator‐associated pneumonia. The novel polymer was impregnated with a photosensitiser using a swell encapsulation method, and activated with laser light; the antibacterial and anti‐adhesive properties were then assessed. Sampling the test surfaces by swabbing and subsequently performing viable counts was shown to provide an adequate estimate of concentration of bacteria on a test surface. The nitrogen‐ and sulfur‐doped titanium dioxide coatings displayed significant photocatalytic activity against Escherichia coli after exposure to a white light source, which demonstrate d a shift in the band gap from the UV to the visible region of the electromagnetic spectrum. Visible light photocatalysis was confirmed on the silver-coated titania thin films when a UV filter was used to block out the minimal UV component of the white light source, in the form of photo‐oxidation of stearic acid, a reduction in the water contact angle and photocatalytic activity against an epidemic strain of meticillin resistant Staphylococcus aureus (EMRSA‐16). This is the first example of unambiguous visible light photocatalysis and photo‐induced superhydrophilicity alongside a titanium dioxide control that shows no activation. A reduction in the viability of EMRSA‐16 adhered onto the surface of the irradiated silver‐coated titania thin films was also demonstrated. A significant reduction in the recovery of Pseudomonas aeruginosa, Stenotrophomonas maltophilia, Acinetobacter baumannii and Candida albicans was observed on TBO-impregnated polymers, after irradiation with a HeNe laser light. A recently isolated clinical strain of P. aeruginosa showed decreased susceptibility to the photo‐activity of the TBO‐impregnated polymers compared with a laboratory type strain. Finally, a significant reduction in the adhesion of P. aeruginosa on the TBO-impregnated polymers was demonstrated after a 3‐step irradiation schedule. A photo‐bleaching effect was noted after light exposure that reduced the antibacterial activity of the polymers, which demonstrates the requirement for further modification to retain the photosensitiser within the polyurethane matrix. These novel materials have the potential to be used as anti‐microbial surfaces in healthcare environments.

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