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The Prevalence of Antibiotic Resistance Genes in US Waterways and Their Relationship to Water Quality and Land Use Indicators
Citation:
Hill, R., S. Keely, N. Brinkman, E. Wheaton, S. Leibowitz, M. Jahne, R. Martin, AND J. Garland. The Prevalence of Antibiotic Resistance Genes in US Waterways and Their Relationship to Water Quality and Land Use Indicators. Annual Meeting of the Society for Freshwater Science, Detroit, MI, May 20 - 24, 2018.
Impact/Purpose:
The US Centers for Disease Control and Prevention and the World Health Organization have both identified antibiotic resistances in pathogenic bacteria as an emerging and serious human health concern. Past research has identified the genes that confer antibiotic resistance in bacteria to specific drugs. The presence of these genes in US waterways is an emerging pollutant of concern and this research seeks to understand the prevalence of these genes in the Nation’s rivers and streams. In addition, this research explored the association of this prevalence with water chemistry and land use indicators. Previous research has shown that human-related alterations to the landscape can increase the prevalence of some antibiotic resistance genes (ARG) in water samples but no study, to our knowledge, has characterized this relationship at a near-continental scale. We found that the concentration of ARGs was related to increased watershed urbanization and agriculture. Furthermore, urbanization and agriculture were more strongly related to ARG concentration than field-sampled water chemistry metrics. We used water samples from the US EPA’s National River and Streams Assessment (NRSA) in these analyses. The spatially-balanced sampling design of the NRSA allows for statistically-valid summaries of ARG concentrations in US rivers and streams. Preliminary summaries found that the median ARG concentrations ranged ~7-76 target molecules/ml, but some samples were as high as 84,633 molecules/ml. This study could provide an important baseline for quantifying the prevalence of these emerging pollutants in the Nation’s waters for future monitoring. This research supports the development of robust national maps of stream conditions, which is of interest to the Monitoring Branch within the Office of Water.
Description:
Antibiotic resistance genes (ARGs) in freshwaters are an emerging contaminant of concern. We used 1,747 water samples from the USEPA’s 2013-2014 National Rivers and Streams Assessment and digital-droplet polymerase chain reaction techniques to quantify the concentrations (target molecules/ml) of several ARGs across the conterminous US. Median ARG concentrations ranged from ~7-76 molecules/ml (max=84,633 molecules/ml). Several ARGs were positively and significantly related to watershed urbanization and agriculture. For example, multiple-regression showed a positive relationship between sul1 (associated with drug-resistant Salmonella) and watershed urbanization and agriculture (multiple-r2=0.34). Likewise, these watershed metrics explained 37% of the variation in intI1, a gene that facilitates development of drug resistance in bacteria. ARG concentrations were also positively correlated with turbidity, total suspended solids, and chloride, ammonia, potassium, and nutrient concentrations, but these relationships were weaker (r2=0.04-0.2) than those found with land use. Hotspot analysis confirmed that ARG concentrations are lower in western mountains and higher in portions of the midwestern and northeastern US with distinct spatial clustering, especially in areas with intensive agriculture. This study provides a baseline for ARG concentrations in the Nation’s streams that could be critical for future monitoring of these emerging contaminants.