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Environ Sci Technol. 2019 Feb 19;53(4):2013-2026. doi: 10.1021/acs.est.8b04393. Epub 2019 Feb 3.

Degradation and Deactivation of Bacterial Antibiotic Resistance Genes during Exposure to Free Chlorine, Monochloramine, Chlorine Dioxide, Ozone, Ultraviolet Light, and Hydroxyl Radical.

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Department of Civil and Environmental Engineering , University of Washington (UW) , Seattle , Washington 98195-2700 , United States.
School of Earth Sciences and Environmental Engineering , Gwangju Institute of Science and Technology (GIST) , Gwangju 61005 , Republic of Korea.


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.


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