EVALUATION OF EFFECTIVENESS OF SWINE MANURE TREATMENT ALTERNATIVES TO MITIGATE ANTIMICROBIAL RESISTANCE

• The effectiveness of five different swine manure treatments for mitigating antimicrobial risk factors was compared. • Anaerobic digestion and liming were found to be the most effective treatments, especially for reducing growth of cells on tetracycline. • Inconsistent outcomes across treatments highlight the complex interplay of antibiotic residues, resistance genes, and microbial growth, and highlight these relationships as targets for further investigation. Swine manure is typically applied to agricultural land at agronomic rates, providing essential nutrients to crops and enhancing soil fertility. While providing nutrients, manure can also introduce pathogens and other contaminants, including antibiotic residues and antibiotic-resistant bacteria (ARB) and genes (ARGs), into the environment with subsequent threats of transfer to humans through the food chain. There are various manure management strategies that may be considered before land application to potentially mitigate the risks of antimicrobial resistance exposure. In a laboratory manure slurry incubation study, the effectiveness of five different manure treatment practices was evaluated. These practices included aeration, anaerobic digestion (AD), heat, liming, and solid-liquid separation (SLS), and were assessed for their ability to reduce antibiotics, antibiotic-resistant bacteria (ARBs), and antibiotic resistance genes (ARGs). This study focused primarily on the impacts on tetracycline (TET), TET-resistant populations, and TET-resistant genes. Additionally, we evaluated the impacts of manure treatments on macrolide (MAC) resistance. We compared the effects of manure treatment on phenotypic resistance of TET, the concentration of TET and MAC residues, and copies of several TET-and MAC-resistant genes. For TET-resistant ARB, our results indicate that AD and liming are the most effective among all treatments. Liming was able to rapidly reduce TET-resistant ARB. Comparing ARGs and antibiotic residuals, we found AD to be the most effective treatment in reducing TET-resistant genes (tetO, tetM, and ermB) and total TET and MAC residues. This research provides valuable insights that can be used to recommend best management practices to farmers and policymakers to reduce dissemination of antimicrobial resistance through environmental pathways.