Prairie strips' effect on transport of antimicrobial resistance indicators in poultry litter.

Poultry litter is a valuable nutrient resource for agricultural production but is also a potential source for introducing antibiotic resistance genes (ARGs) and litter-associated bacteria (LAB) to the environment. Prairie strips have been demonstrated as an effective conservation practice to improve environmental quality in agroecosystems. This research aims to assess prairie strips' potential for reducing the transport of LAB and ARGs in runoff after litter application. Plot-scale rainfall simulations were performed using a replicated block design, with soil and surface runoff samples taken during the rainfall event. Microbial taxa and ARGs were characterized in the litter, soil, and water samples. In plots with litter application, LAB and ARGs were mainly detected in runoff, with very low detection in soils. Detection of ARGs in runoff, irrespective of strip installations, is consistent with previous observations of litter as a source of antimicrobial resistance (AMR) risks. The effectiveness of prairie strips to remove LAB and ARGs varied. In two of the three prairie strip plots, fewer AMR indicators were detected relative to control plots, suggesting that the prairie strips can potentially reduce these risks. In one plot, which was also associated with increased flow rate, we observed increased AMR indicators despite the installation of a prairie strip. Our observations highlight the need to prioritize understanding of soil properties even within the same site. Although we show that prairie strips can potentially reduce AMR risks, further research is needed to better understand the influence of rainfall timing, soil, and litter characteristics.

Antibiotic resistance gene dissipation in soil microcosms amended with antibiotics and swine manure.

The use of antibiotics in animal agriculture has exacerbated the presence of both antibiotic resistance genes (ARGs) and residual antibiotics excreted in animal manure. Field application of this manure is a common practice because its nutrient rich material can benefit crop growth. However, this practice can also introduce antibiotics and ARGs into nonagricultural settings. The integration of prairie buffer strips within and at the edge of crop fields is a potential management solution to reduce concentrations of ARGs commonly transported via water runoff and infiltration. An incubation experiment was conducted to investigate the fate of ARGs in directly manured crop field soils and the surrounding affected prairie strip soils. Row crop and prairie strip soils sampled from three sites received either an antibiotic spike and swine manure addition or a control water addition. The concentrations of select ARGs were then monitored over a 72-d period. Although soil vegetation and site location were not observed to influence ARG dissipation, the select genes did display different half-lives from one another. For example, tetM demonstrated the fastest dissipation of the genes quantified (average half-life, 5.18 d). Conversely, sul1 did not conform to the first-order linear regression kinetics used to describe the other investigated genes and was highly abundant in control prairie strip soils. The quantified half-lives of these select ARGs are comparable to previous studies and can inform monitoring and mitigative efforts aimed at reducing the spread of ARGs in the environment.