Antibacterial activity of novel self-disinfecting surface coatings
, PhD thesis, University of Salford.
The antibacterial activities of different thin films (TiO2/CuO, Cu/SiO2 and Ag/SiO2) prepared by ﬂame-assisted chemical vapour deposition (FACVD) and atmospheric pressure thermal (APT-FCVD) for TiO2/CuO films, were investigated against standard strains of bacteria used for disinfectant testing and against multi-antibiotic resistant bacteria that have been shown to persist in the hospital environment. These included; MRSA strains (EMRSA15 and two recent clinical isolates MRSA 1595 and MRSA 1669), extended spectrum β-lactamase (ESBL) producing Escherichia coli, a second (ESBL- 2 ) producing Escherichia coli, KPC+ (carbapenemase producing) Klebsiella pneumoniae, Stenotrophomonas maltophilia, Acinetobacter baumannii, Listeria monocytogenes, Salmonella enterica ser typhimurium, and vancomycin resistant Enterococcus faecium (VRE) . The Antimicrobial activity of the above coatings (Cu/SiO2 and Ag/SiO2) was investigated based on the BS ISO 22196:2009 and 2011 Plastics – Measurement of antibacterial activity on plastics and other porous surfaces. The activity of TiO2/CuO films was investigated based on the BS ISO 27447:2009 Test method for antibacterial activity of semiconducting photocatalytic materials.
On the TiO2/CuO films, the bacteria were killed by UVA irradiation of the photocatalyst with a >5 log kill within 4-6 h except for the MRSA where a 2.3 log kill was obtained after 6 h increasing to >5 log after 24 h. There was antimicrobial activity in the dark which was enhanced by irradiation with fluorescent light. There was also activity at 5ºC under UVA but activity was lower when fluorescent light was used for illumination. The Cu/SiO2 coating showed a >5 log reduction in viability after 4 h for the disinfectant test strain (E.coli) and for some pathogenic strains include; Acinetobacter baumannii, Klebsiella pneumoniae and Stenotrophomonas maltophilia. However, their activity against the other hospital isolates was slower but still gave a >5 log reduction for extended spectrum β-lactamase producing Escherichia coli and Salmonella enterica typhimurium, and > 2.5 log reduction for vancomycin resistant Enterococcus faecium, Listeria and methicillin resistant Staphylococcus aureus within 24 h. The coating was also active at 5ºC but was slow compared to room temperature. The highest activity of copper /silica films was seen at 35ºC, but bacterial cells were also killed on the control surfaces. The Ag/SiO2 coating was also active against pathogenic bacteria; however the coating was not hard or durable as other coatings used. The activity on natural contamination in an in use test in a toilet facility was also determined for coated ceramic tiles (Cu/SiO2 and Ag/SiO2) and coated steel. The results demonstrated that the tiles were highly active for the first 4 months period and the contamination was reduced by >99.9%. However, tiles lost some of their activity after simulated ageing and washing cycles. The Cu/SiO2 coated ceramic tiles placed in Manchester Royal Infirmary also showed antimicrobial activity and no indicator organisms were detected.
The coatings had a good activity against both standard test strains and clinical isolates. The coatings (copper surfaces in particular), may have applications in health care by maintaining a background antimicrobial activity between standard cleaning and disinfection regimes. They may also have applications in other areas where reduction in microbial environmental contamination is important, for example, in the food industry. However, the optimum composition for use needs to be a balance between activity and durability.
Keywords: TiO2, CuO, Ag, Antimicrobial; Chemical vapour deposition; Copper; Disinfection surface; Pathogenic bacteria (hospital pathogen).
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