Identification of antibiotic-resistance-gene molecular signatures suitable as tracers of pristine river, urban, and agricultural sources.

Animal feeding operations (AFOs) and wastewater treatment plants (WWTPs) are potential sources of antibiotic resistance genes (ARGs) in rivers and/or antibiotics that may select for ARGs in native river bacteria. This study aimed to identify ARG distribution patterns that unambiguously distinguish putative sources of ARG from a native river environment. Such molecular signatures may then be used as tracers of specific anthropogenic sources. Three WWTPs, six AFO lagoons, and three sites along a pristine region of the Cache la Poudre (Poudre) River were compared with respect to the frequency of detection (FOD) of 11 sulfonamide and tetracycline ARGs. Principle-component and correspondence analyses aided in identifying the association of tet(H), tet(Q), tet(S), and tet(T) (tet group HQST) with AFO environments and tet(C), tet(E), and tet(O) (tet group CEO) with WWTPs. Discriminant analysis indicated that both tet group HQST and tet group CEO correctly classified the environments, but only the tet group HQST provided a significant difference in FOD among the environments (p < 0.05). Sul(I) was detected in 100% of the source environments but just once in the pristine Poudre River, which was dominated by tet(M) and tet(W). Tet(W) libraries generated from the pristine Poudre River, WWTPs, and AFO lagoons were also discernible based on restriction fragment length polymorphism and phylogenetic analysis. Thus, a novel approach was developed and demonstrated to be effective for the model river system, taking an important step in advancing the fundamental understanding of ARG transport in the environment.