Reactive oxygen species are involved in inhibition of photoreactivation of <i>Staphylococcus aureus</i> irradiated with 222‐nm Far ultraviolet C

Ultraviolet-C (UV-C) at a wavelength of 254 nm is used for disinfection but cannot be used in dwelling space because it is harmful to the human body, while 222-nm Far UV-C shows germicidal effect and poses little hazardous effect to human. Formation of cyclobutane pyrimidine dimers (CPD) of DNA is a main mechanism of UV-C germicidal effect. CPD formed by irradiation with 254-nm UV-C is repaired and bacterial proliferation is recovered by photoreactivation. In this study, we investigated photoreactivation of Staphylococcus aureus irradiated with 222-nm Far UV-C. The proliferative effect of 222-nm Far UV-C irradiated S. aureus by photoreactivation was inferior to that of irradiated with 254-nm UV-C. The 254-nm UV-C wavelength and 222-nm Far UV-C induced CPD in S. aureus cells, and the same level of CPD was repaired in cells irradiated with either UV-C after photoreactivation. It has been reported that UV-C induces generation of reactive oxygen species (ROS) in bacteria and that ROS oxidize and inactivate a variety of biomolecules in bacteria. This study showed that more ROS-producing S. aureus were observed after irradiation with 222-nm Far UV-C compared with 254-nm UV-C. These results indicate that ROS may be involved in lower recovery of 222-nm Far UV-C irradiated S. aureus by photoreactivation.