This study aimed to identify the ions used in disinfection treatments involving UV-A irradiation and to clarify the mechanism of free radical generation in three combinations of silver ions, Staphylococcus aureus, and UV-A irradiation, for applications in dental implants.Free radicals were analyzed 1 or 4 min after combining various ions (Na, Mg, Al, Ca, Fe, Cu, Zn, Ag, Pt, or Au) with S. aureus, followed by UV-A irradiationThe mechanism of free radical generation from the UV-A irradiation of a mixture of Ag and S. aureus was examined using ESR (ESR), NMR (NMR), X-ray diffraction, and GSH/GSSG ELISA assays.Free radicals were generated from combinations of Na, Mg, Al, Ca, Zn, and Ag ions under UV-A irradiation in bacterial suspensions, with Ag producing the highest yield among all ions.Addnl., the mixture of Fe ions and bacterial suspension generated DMPO-SG.The combination of Ag ions and UV-A irradiation in bacterial suspensions resulted in the production of hydroxyl radicals.Free radicals were also generated from all cellular fractions upon UV-A irradiation in the presence of silver, with a higher yield observed in lipopolysaccharide and peptidoglycan.The combination of silver ions and UV-A irradiation oxidized GSH to GSSG, producing thiol radicals.Silver ions in bacteria act as promoters of UV-A photocatalysis.