Simulated winter incubation of soil and swine manure differentially affects multiple antimicrobial resistance elements

Authors: JURGENS, MADISON - University Of Nebraska; Miller, Daniel; Durso, Lisa; SCHMIDT, AMY - University Of Nebraska

Submitted to: Meeting Abstract
Publication Type: Abstract Only
Publication Acceptance Date: 3/29/2018
Publication Date: 6/17/2018
Citation: Jurgens, M.E., Miller, D.N., Durso, L.M., Schmidt, A.M. 2018. Simulated winter incubation of soil and swine manure differentially affects multiple antimicrobial resistance elements. Meeting Abstract. 3rd Conference on Ecology of Soil Microorganisms. Paper No. 155 p. 153.

Interpretive Summary: A major concern for animal production is that antibiotic use may enrich antibiotic resistant (AR) bacteria and genes in animals and eventual enrichment in the environment after manure application. Late fall manure applications to crop fields is typical with slow decomposition and mineralization during winter and early spring. A laboratory soil incubation study was conducted mimicking swine manure application to soils, and selected AR genes were monitored during simulated 120-day winter incubation with multiple freeze-thaw events. Additionally, the effects of two soil moistures and two manure treatments, control versus hydrated lime alkaline stabilization, were assessed. Fourteen tetracycline resistance genes were initially evaluated; three were detected in soil while manure had eight different genes. By day 120, two manure genes [tet(M) and tet(O)] were still detected in all samples, while four other genes were detected less frequently. Other tetracycline resistance genes were detected rarely, if at all. Four resistance elements [intI1, blactx-m-32, sul(I), erm(B)] and a ribosomal gene were measured using quantitative molecular methods. AR gene relative abundances were initially 100x to 1000x greater in the manure compared to soil, but during the manure/soil incubations abundances decreased 10x to 100x. Alkaline stabilization treatment significantly decreased the relative abundance of intI1, sul(I), and erm(B) while antecedent soil moisture had little effect.

Technical Abstract: A major concern for animal production is that antibiotic use may enrich antibiotic resistant (AR) bacteria and genes in the gastrointestinal tract and with the subsequent application of manure nutrients for row crop production, AR bacteria and genes may become enriched in the environment. In the United States, manure applications to crop fields typically occur during the fall with slow decomposition and mineralization until spring planting season. A laboratory soil incubation study was conducted mimicking swine manure application to soils, and selected AR genes were monitored during simulated 120-day winter incubation with multiple freeze-thaw events. Additionally, the effects of two antecedent soil moistures and two manure treatments, control versus hydrated lime alkaline stabilization (HLAS) were assessed using four replicates per treatment-moisture. Fourteen tetracycline resistance genes were initially evaluated; tet(D), tet(G), and tet(L) were detected in soil while manure contained tet(A), tet(B), tet(C), tet(G), tet(M), tet(O), tet(Q), and tet(X). By day 120, the manure-borne tet(M )and tet(O) were detected in all samples. tet(C), tet(D), tet(L), and tet(X) were detected less frequently. Other tet resistance genes were detected rarely, if at all. Four resistance elements [intI1, blactx-m-32, sul(I), erm(B)] and 16s rRNA were measured using quantitative PCR. AR gene relative abundances were initially 100x to 1000x greater in the manure compared to soil, but in the manure/soil incubations abundance decreased 10x to 100x. The HLAS treatment significantly decreased the relative abundance of intI1, sul(I), and erm(B) during incubation while antecedent soil moisture had little effect.