Development of a standard evaluation method for microbial UV sensitivity using light-emitting diodes

Kai Ishida; Yushi Onoda; Yasuko Kadomura-Ishikawa; Miharu Nagahashi; Michiyo Yamashita; Shiho Fukushima; Toshihiko Aizawa; Shigeharu Yamauchi; Yasuo Fujikawa; Tomotake Tanaka; Takashi Uebanso; Masatake Akutagawa; Kazuaki Mawatari; Akira Takahashi

doi:10.1016/j.heliyon.2024.e27456

Development of a standard evaluation method for microbial UV sensitivity using light-emitting diodes

Heliyon. 2024 Mar 8;10(6):e27456. doi: 10.1016/j.heliyon.2024.e27456. eCollection 2024 Mar 30.

Authors

Kai Ishida¹, Yushi Onoda^{1

2}, Yasuko Kadomura-Ishikawa¹, Miharu Nagahashi³, Michiyo Yamashita³, Shiho Fukushima³, Toshihiko Aizawa², Shigeharu Yamauchi², Yasuo Fujikawa², Tomotake Tanaka², Takashi Uebanso^{1

3}, Masatake Akutagawa⁴, Kazuaki Mawatari^{1

3}, Akira Takahashi^{1

3}

Affiliations

¹ Department of Microbial Control, Institute of Biomedical Sciences, Tokushima University Graduate School, Tokushima, Japan.
² Nichia Corporation, Tokushima, Japan.
³ Department of Preventive Environment and Nutrition, Institute of Biomedical Sciences, Tokushima University Graduate School, Tokushima, Japan.
⁴ Department of Electrical and Electronic Engineering, Graduate School of Technology, Industrial and Social Sciences, University of Tokushima, Tokushima, Japan.

Abstract

Ultraviolet (UV) light is an effective disinfection method. In particular, UV light-emitting diodes (UV-LEDs) are expected to have many applications as light sources owing to their compact form factor and wide range of choices of wavelengths. However, the UV sensitivity of microorganisms for each UV wavelength has not been evaluated comprehensively because standard experimental conditions based on LED characteristics have not been established. Therefore, it is necessary to establish a standard evaluation method based on LED characteristics. Here, we developed a new UV-LED device based on strictly controlled irradiation conditions using LEDs for each wavelength (250-365 nm), checked the validity of the device characteristics and evaluated the UV sensitivity of Escherichia coli using this new evaluation method. For this new device, we considered accurate irradiance, accurate spectra, irradiance uniformity, accurate dose, beam angle, surrounding material reflections, and sample condition. From our results, the following UV irradiation conditions were established as standard: 1 mW/cm² irradiance, bacterial solution with absorbance value of A₆₀₀ = 0.5 diluted 10 times solution, solution volume of 1 mL, working distance (WD) of 100 mm. In order to compare the effects of irradiation under uniform conditions on inactivation of microorganisms, we assessed inactivation effect of E. coli by LED irradiation at each wavelength using the U280 LED as a standard wavelength. The inactivation effect for U280 LED irradiation was -0.95 ± 0.21 log at a dose of 4 mJ/cm². Under this condition of dose, our results showed a high wavelength dependence of the inactivation effect at each UV wavelength peaking at 267 nm. Our study showed that this irradiation system was validated for the standard UV irradiation system and could be contributed to the establishment of food and water hygiene control methods and the development of equipment for the prevention of infectious diseases.

Keywords: Escherichia coli; Microorganism inactivation; Standard evaluation method; UV dose; UV-LEDs.