Cropland amendment with beef cattle manure minimally affects antimicrobial resistance

Authors: Miller, Eric; Spiehs, Mindy; Arthur, Terrance; Woodbury, Bryan; CORTUS, ERIN - University Of Minnesota; CHATTERJEE, AMITAVA - North Dakota State University; RAHMAN, SHAFIQUR - North Dakota State University; Schmidt, John

Submitted to: Journal of Environmental Quality
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/15/2019
Publication Date: 10/10/2019
Publication URL: https://handle.nal.usda.gov/10113/6837736
Citation: Miller, E., Spiehs, M., Arthur, T.M., Woodbury, B., Cortus, E., Chatterjee, A., Rahman, S., Schmidt, J.W. 2019. Cropland amendment with beef cattle manure minimally affects antimicrobial resistance. Journal of Environmental Quality. 48:1683-1693. https://doi.org/10.2134/jeq2019.02.0042.
DOI: https://doi.org/10.2134/jeq2019.02.0042

Interpretive Summary: Concerns have been raised that using beef cattle manure to amend croplands increases amount of antimicrobial resistant bacteria in these soils. If the increases persist until crops are planted this could increase food-animal and human exposures to antimicrobial resistant bacteria through feed and produce. At three farms (one each in Nebraska, North Dakota, and South Dakota) croplands were amended with either: beef cattle manure, inorganic fertilizer, or were not amended (control). Manure amendment did not change the levels of all 8 antimicrobial resistance bacteria measured. Manure amendment did not increase levels for 8 of the 10 antimicrobial resistance genes measured. For the other two antimicrobial resistance genes, AMR increases in manure amendment croplands only occurred at one location, were transient, and generally were within the abundance ranges observed for control croplands. Thus, we conclude that the common practice in U.S. Upper Midwest of region of land applying beef cattle manure likely has minimal impact on environmental antimicrobial resistance levels, feed safety, food safety, animal health, and human health.

Technical Abstract: Concerns exist that beef cattle manure amendment may increase antimicrobial resistance (AMR) in cropland soils and persist over time, potentially increasing food-animal and human exposure via feed and produce. Manure and soil contain many types of antibiotic-resistant bacteria. However, zoonotic pathogens and fecal indicators are most directly linked to human disease and environmental surveillance efforts. We measured the levels of eight antimicrobial resistant zoonotic pathogens and fecal indicators at experimental farms at three locations: Nebraska (silt loam), North Dakota (silty clay), and South Dakota (silty clay loam). Each location had four treatments: beef cattle manure, beef cattle manure with corn stover bedding, inorganic fertilizer, and unamended control. Tetracycline-resistant (TETr), nalidixic- acid resistant, and third-generation cephalosporin-resistant (3GCr) Salmonella enterica were not detected in any cropland samples. Treatments did not significantly affect cropland levels of TETr Escherichia coli, trimethoprim-sulfamethoxazole-resistant E. coli, 3GCr E. coli, TETr Enterococcus spp., or erythromycin-resistant Enterococcus. Additionally, levels of 10 antimicrobial resistance genes (ARGs) were assessed in all soil samples. Except for erm(B) and tet(M) at Nebraska, ARG increases after manure application dissipated before planting occurred. Treatment did not affect the following ARGs: aac(6¢)-Ie-aph(2¢¢)-Ia, aadA1, blaCMY-2, blaCTX-M, mecA, tet(A), and tet(B). The replicated experimental design, quantification data, and paired genotypic and phenotypic information collected for this study can be used to inform risk assessment models. The common US Upper Midwest practice of land applying beef cattle manure in fall does not result in significantly higher levels of the AMR tested in spring cropland soils.