Effect of bromide on the degradation kinetics of antibiotic resistance genes during water chlorination

Abstract

Degradation of antibiotic resistance genes (ARGs) in water chlorination can be influenced by bromide (Br−), a common component in water matrices; however, detailed kinetic information on this process is limited. This study investigated the degradation kinetics tetA and blaTEM-1 genes, contained within the plasmid pWH1266, when exposed to bromine, chlorine, and chlorine with varying concentrations of Br− across a pH range of 7.0–8.5. The degradation of four ARG amplicons, measured using quantitative polymerase chain reaction, was observed to pursue second-order kinetics with bromine, exhibiting k of 4.0 × 102 − 1.6 × 103 M−1 s−1 at pH 7.0 and 2.6 × 102 − 9.6 × 102 M−1 s−1 at pH 8.5. These k values increased linearly with the length of the ARG sequences (209–1136 bps), yielding sequence-independent k of 1.2 and 7.4 × 10−1 (M AT + GC)−1 s−1 at pH 7.0 and 8.5, respectively. The degradation rate of ARGs during chlorination increased with rising Br− concentration due to the bromine formation through the reaction between chlorine with Br−, which subsequently degrades ARGs more rapidly than chlorine. This behavior was successfully simulated using a kinetic model derived from the reaction kinetics of bromine and chlorine reactions with ARGs. The existence of dissolved organic matter extracts only marginally decreased the enhanced degradation of ARGs with Br−, while ammonia significantly inhibited this process during chlorination, both with and without Br−, due to the low reactivity of NH2Cl and NH2Br toward ARGs. These findings highlight the importance of Br− in ARG degradation during water chlorination and the need for further studies in diverse water matrices.