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Degradation and Deactivation of Bacterial Antibiotic Resistance Genes during Exposure to Free Chlorine, Monochloramine, Chlorine Dioxide, Ozone, Ultraviolet Light, and Hydroxyl Radical
- He, Huan, Zhou, Peiran, Shimabuku, Kyle K., Fang, Xuzhi, Li, Shu, Lee, Yunho, Dodd, Michael C.
- Environmental science & technology 2019 v.53 no.4 pp. 2013-2026
- Bacillus subtilis, antibiotic resistance genes, chlorine, chlorine dioxide, disinfectants, disinfection, gene overexpression, hydroxyl radicals, multiple drug resistance, mutation, oxidation, ozone, pH, quantitative polymerase chain reaction, ultraviolet radiation
- This work investigated degradation (measured by qPCR) and biological deactivation (measured by culture-based natural transformation) of extra- and intracellular antibiotic resistance genes (eARGs and iARGs) by free available chlorine (FAC), NH₂Cl, O₃, ClO₂, and UV light (254 nm), and of eARGs by •OH, using a chromosomal ARG (blt) of multidrug-resistant Bacillus subtilis 1A189. Rate constants for degradation of four 266–1017 bp amplicons adjacent to or encompassing the acfA mutation enabling blt overexpression increased in proportion to #AT+GC bps/amplicon, or in proportion to #5′-GG-3′ or 5′-TT-3′ doublets/amplicon, with respective values ranging from 0.59 to 2.3 (×10¹¹ M–¹ s–¹) for •OH, 1.8–6.9 (×10⁴ M–¹ s–¹) for O₃, 3.9–9.2 (×10³ M–¹ s–¹) for FAC, 0.35–1.2(×10¹ M–¹ s–¹) for ClO₂, and 2.0–8.8 (×10–² cm²/mJ) for UV at pH 7, and from 1.7–4.4 M–¹ s–¹ for NH₂Cl at pH 8. For FAC, NH₂Cl, O₃, ClO₂, and UV, ARG deactivation paralleled degradation of amplicons approximating a ∼800–1000 bp acfA-flanking sequence required for natural transformation in B. subtilis, whereas deactivation outpaced degradation for •OH. At practical disinfectant exposures, eARGs and iARGs were ≥90% degraded/deactivated by FAC, O₃, and UV, but recalcitrant to NH₂Cl and ClO₂. iARG degradation/deactivation always lagged cell inactivation. These findings provide a quantitative framework for evaluating ARG fate during disinfection/oxidation, and support using qPCR as a proxy for tracking ARG deactivation under carefully selected circumstances.