Wavelength-dependent differences in survival of Cladosporium sphaerospermum exposed to ultraviolet light

Fungi are one of the main sources of microbial contamination in food and residential environments. There has been reported that fungi are more resistant to drugs than are viruses and bacteria, so efficient sterilization methods are still required. In this study, we examined the effectiveness of ultraviolet (UV) sterilization against mold by focusing on the wavelength and radiant flux dependence of UV. UVC or UVA irradiation inactivated the mold species Cladosporium sphaerospermum in a dose-dependent manner. The energy required to obtain the same inactivation differed significantly between UVC irradiation and UVA irradiation. UVC irradiation induced the formation of substantial amounts of cyclobutane pyrimidine dimers, whereas UVA irradiation did not show any significant difference from the unirradiated group. Furthermore, UVC irradiation induced morphological changes that could be observed by electron microscopy. On the other hand, UVA irradiation suppressed the growth rate. These results suggest that UVC and UVA irradiation have different effects on fungi. The results suggest that both UVC and UVA irradiation may help control fungal contamination. Since the effect of UV differs depending on the wavelength of irradiation, it will be necessary to understand the wavelength-specific effect and use it to control fungal contamination in the living environment. J. Med. Invest. 72 : 260-265, August, 2025.