• bacteria;
  • disinfection;
  • DNA damage;
  • light-emitting diode;
  • ultraviolet irradiation


Aim:  To evaluate the ability of high-energy ultraviolet A (UVA) light-emitting diode (LED) to inactivate bacteria in water and investigate the inactivating mechanism of UVA irradiation.

Methods and Results:  We developed a new disinfection device equipped with high-energy UVA-LED. Inactivation of bacteria was determined by colony-forming assay. Vibrio parahaemolyticus, enteropathogenic Escherichia coli, Staphylococcus aureus and Escherichia coli DH5α were reduced by greater than 5-log10 stages within 75 min at 315 J cm−2 of UVA. Salmonella enteritidis was reduced greater than 4-log10 stages within 160 min at 672 J cm−2 of UVA. The formation of 8-hydroxy-2′-deoxyguanosine in UVA-LED irradiated bacteria was 2·6-fold higher than that of UVC-irradiated bacteria at the same inactivation level. Addition of mannitol, a scavenger of hydroxyl radicals (OH˙), or catalase, an enzyme scavenging hydrogen peroxide (H2O2) to bacterial suspensions significantly suppressed disinfection effect of UVA-LED.

Conclusion:  This disinfection system has enough ability to inactivate bacteria and OH˙ and H2O2 participates in the disinfection mechanism of UVA irradiation.

Significance and Impact of the Study:  We newly developed UVA irradiation system and found that UVA alone was able to disinfect the water efficiently. This will become a useful disinfection system.