Comparative removal of two antibiotic resistant bacteria and genes by the simultaneous use of chlorine and UV irradiation (UV/chlorine): Influence of free radicals on gene degradation

The research aimed to remove antibiotic resistance by the simultaneous use of UV irradiation and chlorine (UV/chlorine). The inactivations of tetracycline resistant bacteria (TRB) during chlorination, UV irradiation, and UV/chlorine was investigated and compared with those of amoxicillin resistant bacteria (AmRB). Similar examination was also conducted for comparing the removals of their resistant genes (i.e., tetM and blaTem). The removals of antibiotic resistance highly depended on chlorine doses and UV intensities. The sufficient chlorine dose (20 mg.L⁻¹) in the chlorination and the UV/chlorine completely inactivated TRB and AmRB (>7.3 log), while the UV irradiation could not achieve the complete disinfection. Microorganisms resistant to different antibiotics exhibit different susceptibility to the disinfection processes. The removals of antibiotic resistant genes (i.e., tetM and blaTem) were more difficult than those of TRB and AmRB. The UV/chlorine was the greatest process for tetM and blaTem removals, followed by chlorination and UV irradiation, respectively. Chlorination decreased the tetM and blaTem by 0.40–1.45 log and 1.04–2.45 log, respectively. The blaTem gene was highly reactive to chlorine, compared with tetM. The UV irradiation caused the tetM and blaTem reductions by 0.32–0.91 log and 0.59–0.96 log, respectively. The UV/chlorine improved the tetM and blaTem removals by 0.98–3.20 log and 1.28–3.36 log, respectively. The •OH contributed to the fraction of tetM and blaTem removals by 48% and 19%, respectively. The effect of reactive chlorine species on the tetM and blaTem removals was minor. The pseudo 1st-order kinetic constants (k′) for tetM and blaTem removals by the UV/chlorine were highest. The •OH enhanced the k′ values by 120% and 20% for the tetM and blaTem removals, respectively. The study showed the potential use of UV/chlorine for controlling antibiotic resistance.