|STALEY, ZACHERY - University Of Nebraska|
|MILLMIER SCHMIDT, AMY - University Of Nebraska|
|ESKRIDGE, KENT - University Of Nebraska|
|LI, XU - University Of Nebraska|
Submitted to: Journal of Environmental Quality
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/27/2019
Publication Date: 6/1/2020
Citation: Staley, Z.R., Millmier Schmidt, A., Woodbury, B.L., Eskridge, K.M., Durso, L.M., Li, X. 2020. Corn stalk residue may add antibiotic-resistant bacteria to manure composting piles. Journal of Environmental Quality. 49(3):745-753. https://doi.org/10.1002/jeq2.20017.
Interpretive Summary: Untreated manure used to fertilize crops has the potential to reduce antibiotic effectiveness by increasing environmental resistance. One method being investigated to treat manure prior to application is composting. Composting is a process where material (bulking agent) high in organic carbon like corn stover is added to manure and then piled in a row. While in the row, the organic material begins to decompose causing the pile to heat up. During this heating process, it was expected the antibiotics and resistant microbes would be inactivated. However, it was found some of the bulking agent added was naturally high in antibiotic resistance. A survey of various bulking agents from different sources was evaluated to determine which ones were not high in antibiotic resistance. It was found the use of pesticides tended to increase bulking agent resistance. Also, it was found certain corn hybrids increase resistance. This study suggests screening the bulking agent for resistance prior to composting for improved inactivation of antibiotic resistance.
Technical Abstract: Manure is commonly used as a fertilizer or soil conditioner; however, land application of untreated manure may introduce pathogens and antibiotic-resistant bacteria (ARB) into the soil, with harmful implications for public health. Composting is a manure management practice wherein a carbon-rich bulking agent, such as corn (Zea mays L.) stalk residue, is added to manure to achieve desirable carbon/nitrogen ratios to facilitate microbial activities and generate enough heat to inactivate pathogens, including antibiotic-resistant pathogens. However, when comparing compost piles and stockpiles for ARB reduction, we noticed that bulking agents added ARB to composting piles and compromised the performance of composting in reducing ARB. We hypothesized that ARB could be prevalent in corn stalk residues, a commonly used bulking agent for composting. To test this hypothesis, corn stalk residue samples throughout Nebraska were surveyed for the presence of ARB. Of the samples tested, 54% were positive for antibiotic-resistant Escherichia coli or enterococci using direct plating or after enrichment. Although not statistically significant, there was a trend wherein the use of pesticides tended to result in a greater prevalence of some ARB. Results from this study suggest that bulking agents can be a source of ARB in manure composting piles and highlight the importance of screening bulking agents for effective ARB reduction in livestock manure during composting.