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ARS Home » Plains Area » Lincoln, Nebraska » Agroecosystem Management Research » Research » Publications at this Location » Publication #317716
Title: Assessment of selected antibiotic resistances in ungrazed native Nebraska prairie soils

Author
item Durso, Lisa
item WEDIN, DAVID - University Of Nebraska
item Gilley, John
item Miller, Daniel
item MARX, DAVID - University Of Nebraska

Submitted to: Journal of Environmental Quality
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 9/8/2015
Publication Date: 12/18/2015
Publication URL: http://handle.nal.usda.gov/10113/5661753
Citation: Durso, L.M., Wedin, D., Gilley, J.E., Miller, D.N., Marx, D.B. 2015. Assessment of selected antibiotic resistances in ungrazed native Nebraska prairie soils. Journal of Environmental Quality. 45:454-462.

Interpretive Summary: When measuring antibiotic resistance on farms and in the environment, it is hard to know how much of that antibiotic resistance is due to use of antibiotic drugs for farm animals, and how much is due to other factors. We know that antibiotic resistance occurs naturally in soils, and in this project we measured the antibiotic resistance in ungrazed native Nebraska prairie soils. The information we collected will help us define what a natural background level of antibiotic resistance is for South Eastern Nebraskan soils. All prairies contained bacteria that were resistant to tetracycline and cefotaxime, and 48% of isolates collected were resistant to two or more antibiotics. Tetracycline and sulfonamide resistance genes were found in all 20 prairies. No correlations were found between either antibiotic resistance and soil physical or chemical parameters. Depending on which measure we used to determine resistance, we found different levels in different prairies. In order to determine impacts of food-animal antibiotic use on resistance, it is essential that background and/or baseline levels of measured parameters be considered, and subtracted out when measuring antibiotic resistance in agroecosystems.

Technical Abstract: Measurements of antibiotic resistance from manure-impacted soils result in conflated data. It is difficult to sort out the features that are a result of human antibiotic use, from the features that are a result of the inherent spatial heterogeneity, complexity and dynamics of antibiotic resistant bacteria and antibiotic resistance genes in soils. This study characterizes native Nebraska prairie soils that have not been impacted by human or food-animal waste products. Soil samples were collected from 20 native Nebraskan prairie sites, enumerated on tetracycline and cefotaxime media, screened for tetracycline-, sulfonamide-, ß-lactamase-, and macrolide-resistance genes, and characterized for soil physical and chemical parameters. Our hypothesis was that the resistance would be similar within and between prairies, regardless of whether it was measured using phenotypic or genotypic assays. All prairies contained bacteria that were resistant to tetracycline and cefotaxime, and 48% of isolates collected were resistant to two or more antibiotics. Most (98%) of the soil samples and all 20 prairies had at least one tetracycline gene. Most frequently detected were tet(D), tet(A) tet(O), tet(L), and tet(B). Sulfonamide genes were detected in 91% of samples. No correlations were found between either phenotypic or genotypic resistance and soil physical or chemical parameters. We observed heterogeneity in baseline measures of antibiotic resistance both within and between prairies. In order to determine impacts of food-animal antibiotic use on resistance, it is essential that background and/or baseline levels of measured parameters be considered, and subtracted out when measuring antibiotic resistance in agroecosystems.