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ARS Home » Midwest Area » Ames, Iowa » National Laboratory for Agriculture and The Environment » Agroecosystems Management Research » Research » Publications at this Location » Publication #371348

Research Project: Agroecosystem Benefits from the Development and Application of New Management Technologies in Agricultural Watersheds

Location: Agroecosystems Management Research

Title: Seasonal variations in export of antibiotic resistance genes and bacteria in runoff from an agricultural watershed in Iowa

Author
item NEHER, TIMOTHY - Iowa State University
item LANYING, MA - Iowa State University
item Moorman, Thomas - Tom
item HOWE, ADINA - Iowa State University
item SOUPIR, MICHELLE - Iowa State University

Submitted to: Science of the Total Environment
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/12/2020
Publication Date: 10/10/2020
Citation: Neher, T.P., Lanying, M., Moorman, T.B., Howe, A., Soupir, M.L. 2020. Seasonal variations in export of antibiotic resistance genes and bacteria in runoff from an agricultural watershed in Iowa. Science of the Total Environment. 738. https://doi.org/10.1016/j.scitotenv.2020.140224.
DOI: https://doi.org/10.1016/j.scitotenv.2020.140224

Interpretive Summary: Antibiotic use in agriculture facilitates the spread of antimicrobial resistance (AMR) in the environment where it can be transported into waterbodies where public exposure increases health risk. Manure application on row crops occurs typically in the spring and fall. This study aimed to monitor multiple areas throughout a small-scale watershed (5,324 ha) during 2017 and 2018 that contain swine and cattle feeding operations and known areas with manure application. The AMR indicators we tested for were tylosin-resistant Enterococcus, tetracycline-resistant Enterococcus, and seven antibiotic resistance genes (ARG). Antibiotic resistant Enterococcus detection in subwatershed outlet waters were greatest in the crop growing season. Conversely, the ARG detection in subwatershed outlet waters was significantly greater during the pre-planting early spring months and post-harvest, which are periods of manure application. Flow was a factor in 2018 with E. coli and Enterococcus significantly correlated (p<0.05) with flow throughout each season and ermB significantly correlated with flow during the post-harvest season. Flow was not a significant factor in 2017. These results show that ARGs are more prevalent in the pre-planting months which hints that spring manure application may deliver the greatest risk to the spread of AMR to downstream areas through flow pathways. This research helps scientists and conservation specialists identify factors that impart the greatest risk for off-site transport of these microbial contaminants.

Technical Abstract: The use of antibiotics in agriculture facilitates the spread of antimicrobial resistance (AMR) in the environment where it can accumulate. Seasonal changes can affect the potential for AMR to mobilize throughout the environment through flow pathways into receiving waterbodies where it has the potential to become a public health risk. Manure application on row crops can serve as a vector in which AMR is introduced into the soil environment and occurs typically in the spring and fall. This study aimed to monitor multiple areas throughout a small-scale watershed (5,324 ha) during 2017 and 2018 that has within it both swine and cattle feeding operations and known areas with manure application. We hypothesized that we will see higher differences in AMR indicators in the pre-planting and post-harvest periods than in the summer growing season because we assume that spring manure application occurs during pre-planting and fall manure application occurs during post-harvest. The AMR indicators we tested for were plate counts for tylosin resistant Enterococcus, tetracycline resistant Enterococcus, and antibiotic resistance gene (ARG) analysis for ermB, ermF (macrolide), tetA, tetM, tetO, tetW (tetracycline), sul1, sul2 (sulfonamide), aadA2 (aminoglycoside), vgaA, and vgaB (pleuromutilin). Our results showed that the growing season favored the plate count results while the pre-planting and post-harvest seasons had significantly higher (p<0.05) ARG indicators, but especially higher in the pre-planting season. Flow was a factor in 2018 with E. coli and Enterococcus significantly correlated (p<0.05) with flow throughout each season and ermB significantly correlated with flow during the post-harvest season. Flow was not a significant factor in 2017. These results show that ARGs are more prevalent in the pre-planting months which hints that spring manure application may deliver the greatest risk to the spread of AMR to downstream areas through flow pathways.