Tracking Sources and Dissemination of Indicator Antibiotic Resistance Genes at a Watershed Scale

Fecal contamination of surface water from anthropogenic sources that contain antibiotic resistance genes (ARGs) poses a potential risk to human health. Therefore, identifying ARG sources is essential for protecting drinking and recreational water. An investigation was undertaken to determine anthropogenic ARG sources in a representative mixed-land-use watershed in the Northeastern United States to examine the relationships between ARGs, microbial source tracking (MST) markers, and in-stream physiochemistry. Monthly water samples were collected from 11 sites throughout one year, including the confluence of key first-order streams representing distinct land-use types. Five anthropogenic indicator ARGs (oqxA, ermB, sul1, mexE, tetO) were monitored to quantify ARG loading and help identify ARG sources. The monitoring efforts revealed that human inputs via sewer, septic failure, or illicit discharge and agriculture were dominant ARG sources. Results also indicated that anthropogenic ARGs were more persistent in the surface water than Escherichia coli or MST markers, suggesting they may integrate into the native microbial community. Understanding the impact of different fecal sources on ARG loading is crucial for developing sustainable and effective watershed management plans to control fecal and ARG contamination and protect drinking and recreational water.