Manure Management Helps Control Prevalence of Antibiotic Resistance Genes, Study Says

Note to Editors: Photos of Amy Pruden-Bagchi and a copy of the full journal article are available with the news release at

Simple modifications in agricultural practices can help diminish the spread of antibiotic resistance genes – a major health concern – in manure, a CSU researcher has found.

Amy Pruden-Bagchi, an assistant professor in the Department of Civil and Environmental Engineering who has received national accolades for her work on antibiotic resistance genes, found that adding organic material such as alfalfa and leaf compost and watering and turning (e.g., composting) reduced the proliferation of the genes. Based on the findings, a treatment time of two to three months is recommended prior to land application to reduce the spread of resistance genes.

The study was reported in a fall 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.

"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, who was recognized by President Bush in November with a Presidential Early Career Award. "My research focuses on how antibiotic resistance genes spread and how we can develop ways to treat them since there are currently no standard practices for removing them from water supplies."

Pruden-Bagchi’s research has demonstrated that drug-resistant DNA itself 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 other cells.

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

Pruden-Bagchi received the Presidential Early Career Award through a nomination by the National Science Foundation for research using molecular biology to investigate the pathways, mitigation and treatment of antibiotic-resistant genes in the environment. In 2006, Pruden-Bagchi was awarded the NSF CAREER award; her research was presented in the January 2007 issue of Scientific American magazine.