Barber, Jodie and Pickup, Roger (2015) Using blue light for bacterial inactivation. Masters thesis, Lancaster University.
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Abstract
Aims. To investigate the inactivation of a range of recently isolated environmental and clinical bacteria using blue light from light emitting diodes (LEDs). Specific objectives. To investigate the impact of the following on bacterial inactivation using a custom-built LED light module: i) exposure time; ii) sample distance; iii) bacterial concentration; iv) sample position on plate; v) incorporation of UV-resistance plasmids and also to conduct comparisons in inactivation efficacy of: i) pulsed versus continuous exposure to 405 nm light and ii) 405 nm versus UV-C. Methods. Bacterial cultures were grown in Tryptone Soya Broth (TSB) and after processing were washed twice prior to re-suspension in Phosphate Buffered Saline (PBS). Following this, dilutions were made and exposed, on agar plates, to blue light (BL, 405 nm) or UV-C light (290 nm - 100 nm ) in a variety of experiments. Results. The results indicated that bacterial inactivation by BL is dose-dependent, the presence of a plasmid encoding UV-resistance genes did not provide protection, and no relationship between inactivation through BL or UV-C could be inferred. Conclusions. Depending on the dose, 405 nm BL was shown to be effective at inactivating the majority of the bacterial species and strains tested. Exceptions were strains belonging to the genus Enterobacter and Raoultella. Overall, there was a broad array of sensitivities across the species used. Significance and Impact of the Study. Results indicate a positive potential future for using BL to inactivate bacteria. More research is required to investigate this at different levels.