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 log₁₀ unit reductions of facultative pathogenic bacteria (FPB), their taxonomic gene markers, and target ARGs. However, the additional effects of TMPyP and H₂O₂ 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 ermB, tetM, sul1, 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 H₂O₂. 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.