Researcher gives horse owners another reason to compost dung

December 20, 2007

Amy Pruden-Bagchi

Horse owners have just been given one further reason to compost their animal's manure - antibiotic resistant genes.

Researchers at Colorado State University found that the simple act of composting dung - adding organic material such as lawn clippings and leaf material, watering, and turning - reduces the proliferation of antiobiotic resistant genes.

Amy Pruden-Bagchi, an assistant professor in the Department of Civil and Environmental Engineering, has shown that drug-resistant DNA is an environmental contaminant.

This is based in part on the fact that, even if cells carrying the genes have been killed, the DNA still winds up in the environment and may get transferred to living cells, even from dung.

Pruden-Bagchi, who described the genes as a major health concern, said simple modifications in agricultural practices could help diminish their spread.

Her research found that adding organic material such as alfalfa (lucerne) and leaf compost and watering and turning (the process of composting) reduced the proliferation of the genes.

Based on the findings, a treatment time of two to three months is recommended to reduce the spread of resistant genes before applying the composted material to land.

Pruden-Bagchi has received accolades in the United States for her work on antibiotic resistant genes.

"More studies are required, but this is a successful first step in determining how we can keep reduce the spread of this new class of contaminant," said Pruden-Bagchi.

"My research focuses on how antibiotic resistant genes spread and how we can develop ways to treat them since there are currently no standard practices for removing them from water supplies."

Her most recent field studies on manure tested the genes' reactions to high-intensity management such as composting and low-intensity management such as stockpiling.

With high-intensity management, researchers added materials to the manure, watered it and turned it. They found that all three antibiotics tested - chlortetracycline, tylosin and monensin - dissipated more rapidly under the high-intensity management conditions.

Tetracycline and sulfonamide are commonly used antibiotics in people and animals.

Antibiotic resistance genes are not regulated, but there is growing interest in understanding and documenting if there are indeed human health effects from antibiotic resistance in water.

They would likely have to exceed the background levels of resistance that are already present in humans and correspond to antibiotics that are critical to fighting antibiotic-resistant diseases in humans.

Pruden-Bagchi has done previous studies on the occurrence of tetracycline and sulfonamide antibiotic resistance genes in sampling sites along the Poudre River. As expected, they found higher concentrations in more populated or heavily farmed areas, but still detected low levels of antibiotic resistance genes in pristine areas as well. Pruden-Bagchi found that treated water and wastewater also carried the genes.

"Microbes carrying these antibiotic resistant genes are not effectively killed by antibiotics, and the presence of these drugs in the environment may stimulate them to proliferate," Pruden-Bagchi said.

The study was reported in the autumn issue of the Journal of Environmental Quality. Other Colorado State authors of the paper included Kenneth Carlson, civil engineering professor; Jessica Davis, professor in the Department of Soil and Crop Sciences; and students Heather Storteboom, Sung-Chul Kim and Kathy Doesken.