"Antibiotic-resistant bacteria are pervasive in streams and rivers downstream of large Wisconsin livestock operations, increasing the risk of superbugs that make people sick and cannot be treated, according to a new study.
The water contamination likely stems from high use of antibiotics in animals housed in concentrated animal feeding operations, or CAFOs, according to the study. While the practice of livestock antibiotic use decreased significantly over the past decade, there was a recent trend reversal in the US: sales and distribution of antibiotics approved for use in food-producing animals increased by 16% between 2023 and 2024 — the highest increase on record, according to a 2024 US Food and Drug Administration (FDA) report.
Wisconsin has an estimated 347 CAFOs — nearly all dairy farms — and is the second-largest dairy producing state. The new study, published in the Journal of Hazardous Materials, adds to evidence that loads of manure from CAFOs are sending harmful bacteria into nearby waterways and contributing to drug-resistance that threatens to render antibiotics ineffective in treating human illness. It is also one of the first studies to analyze the presence of bacteria and drug resistance upstream and downstream of a commercial calf ranch.
Researchers tested water at eight sites in rivers and streams near dairy CAFOs and one site near a calf ranch CAFO. They also took samples from two sites at a lake unaffected by CAFO manure. All of the sites were in eastern Wisconsin, but the study did not identify the waterways or the CAFOs. They looked at Escherichia coli (E. coli), a large group of bacteria that can make people sick, and found that about 70% of E. coli strains near CAFOs were resistant to multiple antibiotic drugs, while just 8% of strains at the sites that were not near CAFOs had multi-drug resistance."
