Abuse of antiobiotics at factory farms threatens the effectiveness of drugs used to treat disease in humans

October 22, 2007

The routine, medically unnecessary use of antibiotics to promote the enhanced growth of livestock is making disease-causing bacteria more resistant to the drugs, which diminishes their power to treat life-threatening diseases in humans.

For centuries, infections like pneumonia and tuberculosis caused by bacteria were a major cause of disease and death. The discovery of antibiotics has proven critical in greatly reducing infectious diseases, and protecting public health relies heavily on the use of these drugs. But repeated exposure to antibiotics enables resistant strains of bacteria to evolve. Some bacteria are naturally resistant, so they survive treatment and multiply.

When antibiotics are given again, the resistant bacteria remain. As the resistant strain within the bacterial population increases over time, the drugs become less effective. The more antibiotics we use, the more likely it is that bacteria will become resistant. The Institute of Medicine, part of the National Academy of Sciences, estimated that the annual cost of treating antibiotic-resistant infections in the U.S. might be as high as $30 billion. (National Institute of Allergy and Infectious Diseases)

The increased use of antibiotics in animal production has gone hand-in-hand with the development of industrial-style livestock operations. Thousands of animals are crammed into the unhygienic, crowded quarters of a typical factory operation, and antibiotics are dispensed constantly through the animals’ feed. Twenty-five million pounds of antibiotics are fed to American livestock annually. This is about 70% of the total amount of antibiotics produced in the U.S. each year and eight times more than the amount used as human medicine. (Union of Concerned Scientists, 2001) Scientists do not understand how or why the drugs promote growth. Many of the same antibiotics — six of the 17 classes of antibiotics — used to promote growth in animals are also used to treat diseases in humans. (The New York Times, 1999)

Evidence is increasingly showing that resistance to treatment, caused by the overuse of antibiotics, threatens public health.

Drug-resistant infections, some of which are fatal, have been increasing in the U.S. population. Many scientists attribute the problem to the misuse of antibiotics in humans and animals. (The New York Times, 1999) Although it is not the only source of the problem, the use of antibiotics to promote livestock growth is a major contributor to antibiotic resistance.

According to the Center for Disease Control, more than one-third of the salmonella poisoning cases in 1997 were found to be resistant to five antibiotics. Drug resistance in campylobacter bacteria, the most commonly known cause of bacterial food-borne illness in the United States, increased from zero in 1991 to 14 percent in 1998. (The New York Times, 1999)

A Harvard University study showed that antibiotic-resistant genes found in bacteria infecting humans were identical to some of the same bacteria infecting animals. (O’Brien et.al., 1982) Scientists at the Center for Disease Control linked an outbreak of antibiotic-resistant salmonella in humans to beef cattle that had been fed subtherapeutic doses of chlortetracycline for growth promotion. (Holmberg, et.al., 1984)

A more recent study by the Universty of California-Berkeley cited the use of antibiotics in livestock as a possible cause for the emergence of drug resistant strains of E.coli that cause female urinary tract infections. Twenty-two percent of the strains collected at the Berkely site were resistant to a common antibiotic used to treat bladder infections. (Yang, 2001)

Staph bacteria, which cause skin, blood, heart valve, and bone infections that can lead to septic shock and death, are becoming increasingly resistant to methicillin, the chief antibiotic used to treat such infections. From 1975 to 1991, the incidence of methicillin-resistant staph bacteria in U.S. hospitals has increased from 2.4 percent to 29 percent. Staph infections are also becoming increasingly resistant to the last line of defense, vancomycin. (Panlilio, 1992)

The European Union, on the recommendation of the World Health Organization, has banned the use of antibiotics to promote the growth of livestock animals when those drugs are also used to treat people. The Center for Disease Control has agreed with this position, but the U.S. government has failed to reduce the threat that ineffective antibiotics pose to human health. (Lieberman, et.al., 1999)



Holmberg, S.D., Osterholm, M.T., Senger, K.A., and Cohen, M.L., “Drug-resistant Salmonella from animals fed antimicrobials.” New England Journal of Medicine 1984; 311:617-622.

Lieberman, Patricia, et.al., “Protecting the Crown Jewels of Medicine. A Strategic Plan to Preserve the Effectiveness of Antibiotics,” Center for Science in the Public Interest, 1999.

National Institute of Allergy and Infectious Diseses, “Antimicrobial Resistance Fact Sheet,” http://www.niaid.nih.gov/factsheets/antimicro.htm. March, 1999.

The New York Times, “A Move to Limit Antibiotic Use In Animal Feed. Fewer Hardy Bacteria in People is U.S. Goal.” March 8, 1999.

O’Brien, T.F., Hopkins, J.D., Gilleece, E.S., Mederios, A.A., Kent, R.L., Blackburn, .O., Holmes, M.B., Reardon, J.P., Vregeront, J.M., Schell, W.L., Christenson, E., Bissett, M.L., and Morse, E.V., Molecular epidemiology of antibiotic resistance in salmonella from animals and human beings in the United States, New England Journal of Medicine 1982; 307: 1-6.

Panlilio, A.L., “Methicillin-resistant Staphylococcus aureus in U.S. Hospitals, 1975-1991, Infection Control Epidemiology,” 1992; 1

Union of Concerned Scientists, “70 Percent of All Antibiotics Given to Healthy Livestock,” http://www.ucsusa.org/releases/01-08-01.html. January 8, 2001.

Yang, Sarah, “New multi-drug resistant strain of E. coli emerges in three distinct regions, new UC Berkeley study finds,” http://www.berkeley.edu/news/media/releases/2001/10/03_virus.html. October 3, 2001.

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