Degradation Kinetics of Antibiotic Resistance Gene of Methicillin-Resistant (MRSA) during Water Disinfection with Chlorine, Ozone, and Ultraviolet Light.

Degradation kinetics of antibiotic resistance genes (ARGs) by free available chlorine (FAC), ozone (O), and UV light (UV) were investigated in phosphate buffered solutions at pH 7 using a chromosomal ARG () of methicillin-resistant (MRSA). For FAC, the degradation rates of extracellular (extra-) were accelerated with increasing FAC exposure, which could be explained by a two-step FAC reaction model. The degradation of extra- by O followed second-order reaction kinetics. The degradation of extra- by UV exhibited tailing kinetics, which could be described by a newly proposed kinetic model considering cyclobutane pyrimidine dimer (CPD) formation, its photoreversal, and irreversible (6-4) photoproduct formation. Measured rate constants for extra- increased linearly with amplicon length for FAC and O, or with number of intrastrand pyrimidine doublets for UV, which enabled prediction of degradation rate constants of extra- amplicons based on sequence length and/or composition. In comparison to those of extra-, the observed degradation rates of intracellular (intra-) were faster for FAC and O at low oxidant exposures but significantly slower at high exposures for FAC and UV. Differences in observed extra- and intracellular kinetics could be due to decreased DNA recovery efficiency and/or the presence of MRSA aggregates protected from disinfectants.