By Diane Schivera
Most people approach the topic of antibiotic resistance with mixed feelings. Many feel it isn’t important to them because they don’t consider using antibiotics. Others use antibiotics without any concern for the consequences. Still others are in the middle, using antibiotics only when absolutely necessary, i.e., in life threatening situations.
This last, critical circumstance is the one where antibiotic resistance can be lethal. One strain of salmonella, for example, is resistant to five of the strongest antibiotics used to treat humans. The strain accounted for 35% of all salmonella poisoning cases in 1997, according to the Centers for Disease Control and Prevention. This antibiotic-resistant bacterium is not a significant threat to a strong person with a healthy immune system, but for a young child, an elderly person or someone with a compromised immune system, it could cause death.
Antibiotic resistance can develop by two methods. One is simply by survival of the fittest. The susceptible bacteria die when the animal is given antibiotic treatment . The bacteria that survive not only live but will proliferate because of the less crowded environment.
The second way in which antibiotic resistance develops is when resistant plasmids (little bits of genetic information) are transferred to unrelated bacteria. For example, plasmids from Eschericia coli in Germany that came from pigs that were treated with the antibiotic noursethricin ended up in the Shigella bacteria that cause dysentery in humans. The plasmids contain the information that gives noursethricin resistance to E. coli, so now the Shigella contain the resistance.
Today, of the 50 million pounds of antibiotics produced in the United States each year, 40% are given to meat animals and 80% of those are given specifically as growth promoters. These subtherapeutic doses of antibiotics are suspected of being a major cause of antibiotic resistance. A new framework is being proposed by the F.D.A. that would limit, somewhat, the use of at least the drugs that have no other alternatives and that are “essential for the treatment of serious or life threatening disease in humans,” although this framework will address only new uses of antibiotics in animal agriculture, not existing uses.
This limit to antibiotic use was attempted by the F.D.A. in 1984, but the attempt failed. As would be expected, the current ruling is being resisted by Congress due to lobbying by drug companies, the American Veterinary Medical Association, and livestock producers. The latter group fears that such a ban would increase the price of meat and discourage consumers from buying it, but such a fear is unrealistic. England banned the agricultural use of antibiotics that are used in humans and of those promoting cross resistance as growth promoters in 1969, and in 1996 Denmark did the same . Both countries have had only a minor rise in meat costs. In Sweden, where growth promoters were banned in 1986, improved management methods have negated the productivity losses that farmers feared.
On March 9, 1999, a petition to rescind approvals of the subtherapeutic uses in livestock of antibiotics used in (or related to those used in) human medicine was submitted by the Environmental Defense Fund and the Union of Concerned Scientists, among others. This petition would help protect us from antibiotic resistance. To support it, write to Dr. Jane Henney, Commissioner, U.S. FDA,5600 Fishers Lane, Room 1471, Rockville, MD 20857.
Rebecca J. Goldburg, Environmental Defense Fund, personal communication.
Stuart B. Levy, M.D., "Multidrug Resistance – A Sign of the Times," The New England Journal of Medicine, vol. 338, no. 19, May 7, 1998.
Report of a WHO meeting, Berlin, Germany, 13-17 October 1997, The Medical Impact of the Use of Antimicrobials in Food Animals
Frederick Angulo, DVM, National Center for Infectious Disease, Centers for Disease Control and Prevention; for a talk entitled “Antimicrobial Agents in Agriculture, Antimicrobial Resistance in Food, Now and in the Future.”
Diane Schivera is the technical assistant for MOFGA, with a special focus on dairy farms. She holds a B.S. in Animal Science and a M.A.T. in Agricultural Education.