Reactive chlorine species drive simultaneous removal of antibiotic resistant bacteria and antibiotic resistance genes by UV-LED/chlorine

Abstract

Antibiotic resistant bacteria (ARB) and antibiotic resistance genes (ARGs) in aquatic environments pose a growing threat to human health. Here we comprehensively evaluated the simultaneous removal of ARB and ARGs by UV-LED/chlorine, using antibiotic resistant E. coli as a model. UV-LED/chlorine achieved a 5.3-log₁₀ reduction of E. coli at a chlorine dosage of 50 μM and a UV fluence of 5 mJ cm^-2, substantially outperforming UV-LED irradiation or chlorination alone. While UV-LED left the cell membrane intact, chlorination and UV-LED/chlorine both caused membrane damage, with the latter inducing severe structural collapse and cell destruction driven by oxidative attack from reactive chlorine species (RCS). When both ARB and ARGs were present, the intracellular and extracellular ARGs showed (3.2–4.0)-log₁₀ and (1.8–1.9)-log₁₀ reductions during UV-LED/chlorine treatment, respectively. RCS contributed to over 50% of deoxynucleoside damage during UV-LED/chlorine treatment, with the major products being pyrimidine dimers, hydroxylated and chlorinated products. Furthermore, UV-LED/chlorine treatment completely suppressed ARB reactivation and reduced ARG transformation efficiency, thereby reducing post-disinfection biological risk. This study elucidates that UV-LED/chlorine treatment simultaneously inactivates ARB and removes ARGs, overcoming the limitations of UV-LED irradiation and chlorination alone, and offers a robust strategy for mitigating antibiotic resistance in water treatment.