Agricultural wastewater modeling shows that foot baths are a source of antimicrobial resistance

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New research has mapped wastewater flows on farms and revealed where spikes in antibiotic-resistant bacteria are occurring in slurry. This shows that water from copper and zinc foot baths used by dairy animals can cause fluctuations.

Researchers from the University of Nottingham developed mathematical models and conducted on-farm research to investigate the impact of wastewater flows and management practices on antimicrobial resistance (AMR) in slurry. The study is the first to investigate the effects of farm layout, the business practices associated with different parts of the farm, and the impact these can have on the emergence and spread of AMR across the farm.

Transient fluctuations in cephalosporin-resistant Escherichia coli were observed and attributed to agricultural activities, particularly the discharge of spent copper and zinc footbath into the manure system. The results have been published in npj Antimicrobials and resistance.

The results highlight company-specific opportunities to reduce AMR pollution in addition to reducing antibiotic use, including careful disposal or recycling of antimicrobial metal waste.

If not stored properly, dairy manure can be a source of environmental contamination containing antimicrobial resistance genes and bacteria, which can ultimately enter the human population through water or crops.

Previous modeling research from the University of Nottingham showed that manure tanks left alone for at least 60 days without further waste being added reduced the spread of antibiotic resistant bacteria (ARB) as the bacteria died in the hostile environment. Researchers also noticed that there were times when there were spikes in cephalosporin-resistant Escherichia coli.

“What we initially discovered was that the manure tank was not as scary a place as we thought for the spread of antimicrobial resistance genes, and that the bacteria, if left alone for a while, would live in such a hostile environment die.” What was also interesting, however, was that we saw fluctuations in a particularly problematic drug-resistant bacteria called Escherichia coli.

“When we investigated this further in this study using computer models and on-farm research, we saw that there was a direct correlation between the discharge of the water from the zinc and copper foot baths into the manure tank and a peak in the presence of Escherichia coli. said Dov Stekel, Professor of Computational Biology at the University of Nottingham’s School of Biosciences.

In addition to antibiotics, other antimicrobials such as metals (copper and zinc) and other chemicals (e.g. formalin, disinfectants) are widely used on farms around the world, especially in foot baths to prevent lameness in livestock.

“It is known that metals and other antimicrobials (such as formalin and glutaraldehyde) have a co-selective effect on antibiotic resistance, meaning that ARBs can persist in the slurry even after the antibiotics have broken down,” says Dr. Jon Hobman, associate professor. of Microbiology, School of Biosciences.

Professor Stekel added: “By mapping antibiotic-resistant bacteria in this way, we can understand their precise source and, importantly, their route through the farm. We hope this information will lead to wastewater management practices that can be developed to alleviate this.”

Engineers from the University of Nottingham have started investigating how to remove copper and zinc from cattle footbath wastewater and have found that layered double hydroxides successfully removed copper and zinc from cattle footbath. This was the first successful study of the removal of copper and zinc from a commercially available powder mix solution for bovine foot baths.

More information:
Henry Todman et al., Modeling the impact of wastewater flows and management practices on antimicrobial resistance on dairy farms, npj Antimicrobials and resistance (2024). DOI: 10.1038/s44259-024-00029-4

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