Metagenomic Characterization of Antibiotic Resistance Genes in Full-Scale Reclaimed Water Distribution Systems and Corresponding Potable Systems

Water
reclamation provides a valuable resource for meeting nonpotable
water demands. However, little is known about the potential for wastewater
reuse to disseminate antibiotic resistance genes (ARGs). Here, samples
were collected seasonally in 2014–2015 from four U.S. utilities’
reclaimed and potable water distribution systems before treatment,
after treatment, and at five points of use (POU). Shotgun metagenomic
sequencing was used to profile the resistome (i.e., full contingent
of ARGs) of a subset (n = 38) of samples. Four ARGs
(qnrA, blaTEM, vanA, sul1) were quantified by quantitative
polymerase chain reaction. Bacterial community composition (via 16S
rRNA gene amplicon sequencing), horizontal gene transfer (via quantification
of intI1 integrase and plasmid genes), and selection
pressure (via detection of metals and antibiotics) were investigated
as potential factors governing the presence of ARGs. Certain ARGs
were elevated in all (sul1; p ≤
0.0011) or some (blaTEM, qnrA; p ≤ 0.0145) reclaimed POU samples compared
to corresponding potable samples. Bacterial community composition
was weakly correlated with ARGs (Adonis, R2 = 0.1424–0.1734)
and associations were noted between 193 ARGs and plasmid-associated
genes. This study establishes that reclaimed water could convey greater
abundances of certain ARGs than potable waters and provides observations
regarding factors that likely control ARG occurrence in reclaimed
water systems.