Removal of antibiotic resistance genes by Cl2-UV process: Direct UV damage outweighs free radicals in effectiveness

Antibiotic resistance genes (ARGs) pose significant environmental health problems and have become a major global concern. This study investigated the efficacy and mechanism of the Cl2-UV process (chlorine followed by UV irradiation) for removing ARGs in various forms. The Cl2-UV process caused irreversible damage to nearly all ARB at typical disinfectant dosages. In solutions containing only extracellular ARGs (eARGs), the Cl2-UV process achieved over 99.0 % degradation of eARGs. When both eARGs and intracellular ARGs (iARGs) were present, the process reached a 97.2 % removal rate for iARGs. While the abundance of eARGs initially increased due to the release of iARGs from lysed cells during pre-chlorination, subsequent UV irradiation rapidly degraded the released eARGs, restoring their abundance to near-initial levels by the end of the Cl2-UV process. Analysis of the roles in degrading eARGs and iARGs during the Cl2-UV process revealed that UV, rather than free radicals, was the dominant factor causing ARG damage. Pre-chlorination enhanced direct UV damage to eARGs and iARGs by altering plasmid conformation and promoting efficient damage to high UV-absorbing cellular components. Furthermore, no further natural transformation of residual ARGs occurred following the Cl2-UV treatment. This study demonstrated strong evidence for the effectiveness of the Cl2-UV process in controlling antibiotic resistance.