Inactivating facultative pathogen bacteria and antibiotic resistance genes in wastewater using blue light irradiation combined with a photosensitizer and hydrogen peroxide

The effectiveness of antimicrobial blue light (aBL) irradiation in eliminating ten clinically significant antibiotic resistance genes (ARGs) and four taxonomic marker genes of the WHO-priority ESKAPE bacteria group from wastewater treatment plant (WWTP) effluent was examined. Experiments were conducted using an LED-driven continuous-flow photoreactor operating at wavelengths of 405 nm, 420 nm, and 460 nm. Irradiation with aBL alone was insufficient for effectively inactivating or eliminating ESKAPE bacteria and clinically relevant ARGs. The addition of the porphyrin-based photosensitizer TMPyP (10 −6 M) or the oxidative agent H₂O₂ (1 mM) resulted in several log 10 unit reductions of facultative pathogenic bacteria (FPB), their taxonomic gene markers, and target ARGs. However, the additional effects of TMPyP and H 2 O 2 were only noticeable in conjunction with aBL irradiation, as they were ineffective without it. The reduction of the different FPB and ARGs in WWTP effluents was analyzed using culturing and qPCR together with living/dead discrimination. Different FPB and ARGs showed varying susceptibility to aBL-mediated irradiation. Among the FPB, enterococci were the most sensitive, while among the ARGs bacteria carrying erm B, tet M, sul 1, and bla VIM genes exhibited the strongest removal. This sensitivity may be due to the gene-carrying microorganism's response to aBL irradiation combined with TMPyP or H 2 O 2 . Additionally, molecular biology results revealed that aBL irradiation induced up to 13 lesions per 10 kb DNA, which is hypothesized to contribute to the acute inactivation effect and prevent regrowth by inhibiting DNA repair activities. • Antimicrobial blue light (aBL) reduced ESKAPE bacteria and antibiotic resistances. • Photosensitizers and oxidative agents significantly enhanced decontamination. • Gram-positive bacteria were more sensitive to aBL irradiation. • Bacteria carrying erm B, tet M, sul 1, or bla VIM genes showed the highest reductions. • About 13 DNA lesions per 10 kb were detected contributing to bacterial inactivation.