AUTHOR=Fahrenfeld Nicole L., Ma Yanjun , O'Brien Maureen , Pruden Amy 

TITLE=Reclaimed water as a reservoir of antibiotic resistance genes: distribution system and irrigation implications

JOURNAL=Frontiers in Microbiology

VOLUME=4

YEAR=2013

URL=https://www.frontiersin.org/journals/microbiology/articles/10.3389/fmicb.2013.00130

DOI=10.3389/fmicb.2013.00130

ISSN=1664-302X

ABSTRACT=<p>Treated wastewater is increasingly being reused to achieve sustainable water management in arid regions. The objective of this study was to quantify the distribution of antibiotic resistance genes (ARGs) in recycled water, particularly after it has passed through the distribution system, and to consider point-of-use implications for soil irrigation. Three separate reclaimed wastewater distribution systems in the western U.S. were examined. Quantitative polymerase chain reaction (qPCR) was used to quantify ARGs corresponding to resistance to sulfonamides (<italic>sul</italic>1, <italic>sul</italic>2), macrolides (<italic>erm</italic>F), tetracycline [<italic>tet</italic>(A), <italic>tet</italic>(O)], glycopeptides (<italic>van</italic>A), and methicillin (<italic>mec</italic>A), in addition to genes present in waterborne pathogens <italic>Legionella pneumophila</italic> (L<italic>mip</italic>), <italic>Escherichia coli</italic> (<italic>gad</italic>AB), and <italic>Pseudomonas aeruginosa</italic> (<italic>ecf</italic>x, <italic>gyr</italic>B). In a parallel lab study, the effect of irrigating an agricultural soil with secondary, chlorinated, or dechlorinated wastewater effluent was examined in batch microcosms. A broader range of ARGs were detected after the reclaimed water passed through the distribution systems, highlighting the importance of considering bacterial re-growth and the overall water quality at the point of use (POU). Screening for pathogens with qPCR indicated presence of L<italic>mip</italic> and <italic>gad</italic>AB genes, but not <italic>ecf</italic>x or <italic>gyr</italic>B. In the lab study, chlorination was observed to reduce 16S rRNA and <italic>sul</italic>2 gene copies in the wastewater effluent, while dechlorination had no apparent effect. ARGs levels did not change with time in soil slurries incubated after a single irrigation event with any of the effluents. However, when irrigated repeatedly with secondary wastewater effluent (not chlorinated or dechlorinated), elevated levels of <italic>sul</italic>1 and <italic>sul</italic>2 were observed. This study suggests that reclaimed water may be an important reservoir of ARGs, especially at the POU, and that attention should be directed toward the fate of ARGs in irrigation water and the implications for human health.</p>