| Summary: | Control of contaminant microorganisms is important in many different settings, particularly in healthcare and food production and processing, where environmental contamination by pathogenic microorganisms can be detrimental to human health. In the UK, the number of hospital-associated infections (HAI) and food-related illnesses continues to rise. As such, alternative and complementary disinfection and decontamination technologies are constantly being sought. This investigation examined the inactivation efficacy of High-Intensity Narrow Spectrum Light (HINS-light) on a wide range of microorganisms using LED arrays that emitted intense 405-nm light. The theorised inactivation mechanism involves 405-nm stimulation of endogenous porphyrins, ultimately leading to production of reactive oxygen species (ROS) that cause oxidative cell damage and microbial inactivation. All tested microorganisms associated with HAI and foodborne illnesses were readily inactivated by 405-nm light. It was als o established, for the first time, that 405-nm light was germicidal to eukaryotic microorganisms, including Candida albicans, Saccharomyces cerevisiae and the spore-forming fungus Aspergillus niger. Further examination found 405-nm light induced toxic photo-product formation in Nutrient Broth. The photo-product was particularly toxic to Staphylococcus aureus, methicillin-resistant S. aureus (MRSA) and Acinetobacter baumannii, although it elicited either no effect or a bacterio-static effect in other tested bacteria. HINS-light is known to be less germicidal than pulsed ultraviolet (PUV) light produced from a Xenon flashlamp, however this study has demonstrated that sublethally PUV-damaged S. aureus cells can undergo photoreactivation upon exposure to 300-500-nm light, with maximum effect elicited at 360-380 nm. This photoreactivation potential, that can affect the inactivation capability of UV-light decontamination technologies, was not found to be associated with HINS-light treatment. In addition, HINS-light technology has significant safety advantages over UV light thereby permitting its use in occupied environments. This study has greatly extended the range of microorganisms that have been shown to be sensitive to HINSlight exposure, including important pathogens and food spoilage micoorganisms. The study has confirmed that HINS-light has the capability to be used for the control of a wide range of microorganisms in environmental decontamination applications, and thereby has the potential to contribute to an overall reduction in the numbers of HAI and foodborne illnesses.
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