Citation:

Keely, S. National scale studies aid our understanding of the drivers of antimicrobial resistance genes in US waters. VIRTUAL EMERGING CONTAMINANTS SHORT COURSE 2022 by Marquette University, Milwaukee, WI, October 25, 2022.

Impact/Purpose:

The national- and ecoregional scale patterns of several antimicrobial resistance genes, fecal indicator bacteria and anthropogenic indicator (intI1) measured in US rivers and streams are described. Associations of gene concentrations with fecal pollution, watershed integrity and urbanization are evaluated. Gene concentrations will be compared to the same gene occurrences in the next NRSA cycle.

Description:

The discovery of antimicrobials some 80 years ago ushered in a new era of reduced morbidity and mortality due to human infections. In recent years, however, there has been a tradeoff between the benefits of these drugs and their overuse, which has contributed to the evolution of antimicrobial resistance genes (ARG) and increased spread of antimicrobial resistance (AR) bacterial infections in human and animals. The unfortunate spread of ARG has resulted in 2.8 million individuals developing AR infections annually, resulting in 35000 deaths in the US. Not surprisingly, there is also increased spread of AR in the environment that is largely driven by urbanization and agriculture, which may lead to exacerbations in the annual rate of human and animal AR infections. Rivers and streams near wastewater treatment plants, animal feeding operations, or sources of manure and municipal biosolids exhibit elevated ARGs. To better understand the distribution of ARGs in US waters, we used a stratified, probabilistic survey of nearly 2,000 sites that represents 1.2 million kilometers of rivers and streams. Using standardized field methods, field crews collected river and stream environmental samples over the course of 2 years to collect information on key indicators of biological, chemical, and physical condition. We measured the quantities of the class I integron Integrase gene (intI1), several ARGs (e.g. sul1, blaTEM and tetW) and two fecal bacteria indicators using droplet digital PCR. We observed striking geographical patterns for these genes, which were typically higher in eastern regions than western regions. Fecal pollution was associated with the distribution of tetW; urbanization, watershed condition, and outpatient prescription rates were associated with intI1 and sul1. These results suggest that environmental drivers, overuse of antimicrobials, and pollution influence the concentrations of ARGs in US waters. This study is the first of a series of national surveys to monitor ARGs in rivers and streams in the US.

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