Antibiotic Resistance Traced from Hog Farms to Groundwater

U of I study shows tetracycline migration from hogs to groundwater has broad implications for human and ecological health.

The routine use of hog antibiotics can have unintended consequences, with antibiotic resistance genes sometimes leaking from waste lagoons into groundwater.

In a new study, researchers at the University of Illinois report some genes found in hog waste lagoons are transferred – "like batons" – from one bacterial species to another. The researchers found that this migration across species and into new environments sometimes dilutes – and sometimes amplifies – genes conferring antibiotic resistance.

The new report, in the August issue of Applied and Environmental Microbiology, tracks the passage of tetracycline resistance genes from hog waste lagoons into groundwater wells at two Illinois hog operations.

This is the first study to take a broad sample of tetracycline resistance genes in a landscape dominated by hog farms, said R.I. Mackie, professor in the U of I department of animal sciences. And it is one of the first to survey the genes directly rather than focusing on the host organisms.

"If the genes are there, potentially they can get into the right organism at the right time and confer resistance to an antibiotic that's being used to treat disease," Mackie said.

Tetracycline is widely used in swine production to treat or prevent disease, and is commonly used as a feed additive to boost animals' growth. Its near-continuous use in some hog farms promotes the evolution of tetracycline-resistant strains in the animals' digestive tracts and manure.

The migration of antibiotic resistance from animal feeding operations into groundwater has broad implications for human and ecological health. The U.S. has roughly 238,000 animal feeding operations, which generate about 500 million tons of manure per year. Groundwater comprises about 40% of the public water supply, and more than 97% of the drinking water used in rural areas.

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