Date: July 9, 1998
Contacts: Molly Galvin, Media Relations Officer
Kristen Nye, Media Relations Assistant
(202) 334-2138; e-mail <>

Antibiotic Use in Food Animals
Contributes to Microbe Resistance

WASHINGTON -- Bacteria that resist antibiotics can be passed from food animals to humans, but not enough is known to determine the public health risks posed by such transmission, says a new report by a committee of the National Research Council. The federal government should form an oversight panel to ensure the appropriate use of antibiotics in animals and humans, and establish a national database to monitor microbe-related illnesses and trends in antibiotic resistance that may result from drug use in food animals.

"Using antibiotics to control and treat diseases in animals improves the safety of our food supply by providing healthier sources of meat, cheese, milk, and eggs," said committee chair James Coffman, provost, Kansas State University, Manhattan. "But there have been a few cases in which resistant bacteria have been passed to people. Extra vigilance is needed to prevent the spread of bacteria that cannot be destroyed with currently available drugs. And agricultural producers, health care providers, veterinarians, and consumers must use antibiotics properly and be aware of potential risks."

Antibiotic resistance in humans and animals has risen sharply during the last several decades, says the report The Use of Drugs in Food Animals: Benefits and Risks. Some 30 antibiotics -- such as tetracycline, penicillin, and streptomycin -- are approved by the Food and Drug Administration (FDA) for many uses in food animals, and several of the drugs also are used to treat people. Bacteria eventually develop resistance to antibiotics in many ways, such as by creating chemicals that degrade a drug's potency. Resistance can develop rapidly, and it may be transferred in bits of DNA from one bacterium to another and between different species of bacteria.

Potentially life-threatening microbes that can be passed from animals to humans include salmonella and E. coli. Bacteria is transmitted in food products or through direct contact with animals or manure. Infants, the elderly, and others with weakened immune systems are at higher risk from drug-resistant infections, as are farm workers.

A national database on antibiotic use and resistance trends should be created to provide easily accessible data to farm producers, veterinarians, doctors, and other interest groups, the committee said. An oversight panel of representatives from regulatory agencies, the veterinary and medical communities, agriculture production, and consumer groups should regularly monitor information on resistance and make recommendations on how antibiotics should be used in humans and food animals. To maintain an effective supply of antibiotics, the panel would help determine whether new antibiotics should be held in reserve for medical use only, or for specific uses in animals. For example, the veterinary use of fluoroquinolones is now limited by the FDA to prescription-only use in poultry, because the antimicrobial agents could be needed to treat life-threatening infections in humans that don't respond to other antibiotics.

The number of cases of human illnesses that can be traced to antibiotic-resistant germs in food animals is very low, the report says. However, assessing the likelihood that human diseases might be triggered in this way is difficult because critical data are lacking in areas such as sources of illness and shifts in disease rates. In addition, the majority of human diseases caused by microbes in animals are passed through contaminated food products, further complicating assessments of potential health risks. Antibiotic-resistant bacteria -- or any food-borne bacteria -- is unlikely to cause human illness unless the microbes are spread through improper food processing, storing, or cooking, the committee said.

Research to develop new classes of antibiotics should receive more funding, the report says, because bacteria that develop resistance to one antibiotic may become resistant to others in the same class. New drugs will be needed for both the medical and veterinary communities to ensure that alternatives are available to treat antibiotic-resistant infections. To prolong the effectiveness of existing antibiotics, public-education campaigns that stress their proper use should be implemented, the committee said. Resistance is more likely to occur because of misuses in human medicine. In addition, the committee said, consumers should be informed of the benefits and potential risks of antibiotics in food animals.

Drug Monitoring

The committee reviewed the major classes of drugs used for animal health, including antibiotics, antiseptics and fungicides, steroid growth promoters, and antiparasite drugs. Because of a documented increase of antibiotic resistance in human and animals, the committee focused primarily on antibiotics.

Current monitoring systems to detect drugs in milk, meat, and other food products derived from animals are adequate, the committee said. Screening and monitoring techniques should continue to be deployed to protect consumers against the possible adverse effects of ingesting residues of drugs, some of which could be toxic or lead to diseases or allergic reactions. The accuracy of testing techniques should be improved to reduce the number of false-positive results that occur, especially in milk, and more resources are needed to develop testing methods for a wider range of drugs.

In certain cases and with accurate documentation, veterinarians are allowed to prescribe antibiotics to treat animal illnesses other than those specified by the FDA. To ensure that the residues of these drugs are safely reduced in animal tissues before any food products are produced, the agency should develop ranges for safe dosages and establish withdrawal times, the committee said.

Antibiotics in Food Production

Some 60 percent to 80 percent of all cattle, sheep, swine, and poultry in the United States will be given antibiotics at some point. In addition to treating specific diseases, much of the approximately 19 million pounds of antibiotics used annually in agriculture are added to feed or water to promote growth and to help prevent animals in close quarters from transmitting diseases. In these cases, antibiotics are administered in doses much lower than those required to treat specific infections. Using antibiotics in this "subtherapeutic" way allows more animals to be raised at lower costs.

Because these animals are regularly exposed to small doses of antibiotics, any microbes they carry may be more prone to developing resistance. But it is difficult to determine whether or how low doses cause resistance, the report says, because the doses and cycles by which antibiotics are administered vary widely. More data are needed on bacteria-resistance patterns in animals that are treated with antibiotics at specific doses, and how different levels of antibiotic use in animals affect human health. Resistance should be classified by each antibiotic used, the microbes that are affected, levels of resistance, and individual dose and treatment periods.

To reduce the likelihood of resistance, some interest groups have called for banning antibiotic use in food animals for any purpose other than treating specific diseases. The Research Council committee estimated that such a ban would cost consumers about $1.2 billion to $2.5 billion a year -- or $4.85 to $9.72 per person -- in higher prices for poultry, beef, and fish. However, animal diseases might become more widespread, which could increase public health risks and lead to higher demand for antibiotics to treat sick animals. The costs of banning subtherapeutic uses of antibiotics should be weighed against consumer benefits that result from healthier farm animals, the committee said.

The FDA and the U.S. Department of Agriculture approve, regulate, and monitor new animal drugs. FDA should continue to expedite drug-approval review by initiating an arbitration process to settle scientific and regulatory disputes quickly, the committee said. The agency also should review data on drugs already approved and used in other countries. Requirements for drug development and review worldwide should be uniform to shorten the approval process.

Alternatives to Antibiotics

Improved animal-management practices could substantially reduce the amount of drugs needed for food animals, the report says. More research is needed on the impact of nutrition and drug treatments to boost immune function and disease resistance in animals. For example, dietary protein hormone treatments, antioxidant vitamins, and trace elements show promise in maintaining animal immune response. In addition, new vaccination techniques also are needed to prevent the spread of diseases, the report says. Effective vaccines will reduce the demand for antibiotics.

The study was funded by the U.S. Department of Agriculture, and the Department of Health and Human Services, the Pew Charitable Trusts, the American Veterinary Medical Association, and the American Feed Industry Association. The National Research Council is the principal operating arm of the National Academy of Sciences and the National Academy of Engineering. It is a private, non-profit institution that provides independent advice on science and technology issues under a congressional charter. A committee roster follows.

Read the full text of The Use of Drugs in Food Animals: Benefits and Risks  are available at or by calling 202-334-3313  or 1-800-624-6242.  Reporters may obtain a pre-publication copy from the Office of News and Public Information at the letterhead address (contacts listed above).

Board on Agriculture


Food and Nutrition Board

Committee on Drug Use in Food Animals
James R. Coffman(chair)
Kansas State University

George W. Beran
Department of Microbiology
College of Veterinary Medicine
Iowa State University

Harvey R. Colten*
Dean and Vice President for Medical Affairs
Northwestern University Medical School

Connie Greig
Independent Consultant
Little Acorn Ranch
Estherville, Iowa

Jean Halloran
Consumer Policy Institute
Consumers Union of United States Inc.
Yonkers, N.Y.

Dermot Hayes
Associate Professor
Department of Economics
Iowa State University

John B. Kaneene
Professor of Epidemiology and Director, Population Medicine Center
Michigan State University
East Lansing

Kristen McNutt
Consumer Choices Inc.
Winfield, Ill.

David L. Meeker
Swine Research Center
Ohio State University

Stephen C. Nickerson
Mastitis Research Laboratory
Hill Farm Research Station
Louisiana State University Agricultural Center

Thomas Seay
Atlanta Cancer Care

R. Gregory Stewart
Poultry Business Unit
Bayer Animal Health Inc.
Watkinsville, Ga.


Michael J. Phillips, Program Director
Theodore H. Elsasser, Project Director

* Member, Institute of Medicine