Degradation Kinetics of Antibiotic Resistance Gene <i>mecA</i> of Methicillin-Resistant <i>Staphylococcus aureus</i> (MRSA) during Water Disinfection with Chlorine, Ozone, and Ultraviolet Light

Abstract

Degradation kinetics of antibiotic resistance genes (ARGs) by free available chlorine (FAC), ozone (O₃), and UV₂₅₄ light (UV) were investigated in phosphate buffered solutions at pH 7 using a chromosomal ARG (<i>mecA</i>) of methicillin-resistant <i>Staphylococcus aureus</i> (MRSA). For FAC, the degradation rates of extracellular <i>mecA</i> (extra-<i>mecA</i>) were accelerated with increasing FAC exposure, which could be explained by a two-step FAC reaction model. The degradation of extra-<i>mecA</i> by O₃ followed second-order reaction kinetics. The degradation of extra-<i>mecA</i> 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-<i>mecA</i> increased linearly with amplicon length for FAC and O₃, or with number of intrastrand pyrimidine doublets for UV, which enabled prediction of degradation rate constants of extra-<i>mecA</i> amplicons based on sequence length and/or composition. In comparison to those of extra-<i>mecA</i>, the observed degradation rates of intracellular <i>mecA</i> (intra-<i>mecA</i>) were faster for FAC and O₃ 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.