The widespread use of antibiotics in animal husbandry, many scientists believe, contributes to the spread of dangerous drug-resistant bacteria that ultimately infect humans. Now, three studies published simultaneously in the 18 October issue of The New England Journal of Medicine give them new ammunition. Some experts are calling for a rapid end to the practice.
An estimated 12.1 millions of kilos of antibiotics are fed to cattle, chicken, and poultry each year in the U.S. alone--the vast majority not to treat infections, but to help animals gain weight fast. Public health workers argue that this practice can breed drug resistance in pathogens residing in meat, such as Salmonella, Campylobacter, and E. coli, making it difficult or even impossible to treat people who are infected with them. But animal-drug makers and the livestock industry have downplayed the risk and lobbied to hold off restrictions on the drugs (Science, 5 May 2000, p. 792).
Now, Frederick Angulo of the U.S. Centers for Disease Control and Prevention in Atlanta and his colleagues report that 17% of chickens sold in supermarkets had strains of Enterococcus faecium that eluded a drug called quinupristin-dalfopristin, which was approved recently to treat potentially life-threatening infections in hospital patients with weakened immune systems. The resistant microbes probably arose on the farm, they write, because gut microbes in chickens fed a chemically similar drug, virginiamycin, are known to develop quinupristin-dalfopristin resistance. In a second study, a team led by Niels Frimodt-Møller of the Danish Veterinary Laboratory in Copenhagen showed that drug-resistant strains of the same microbe, isolated from supermarket cuts of chicken, grew well in the guts of healthy human volunteers.
Meanwhile, David White of the U.S. Food and Drug Administration (FDA) in Laurel, Maryland, and his colleagues found that 20% of ground-meat samples bought in Washington, D.C., area supermarkets were contaminated with strains of Salmonella, a microbe that can cause life-threatening infections. More than 80% of the strains resisted at least one antibiotic prescribed by doctors; several were insensitive to a drug called ceftriaxone, which is used to treat particularly fierce infections in children.
The results provide a "smoking gun" that links antibiotic use on the farm to human health threats, writes Sherwood Gorbach of Tufts University School of Medicine in Boston in an outspoken editorial in the same issue. The upshot is clear, Gorbach argues: It's time to stop using antibiotics in animal feed.
Nonsense, says Ron Phillips, spokesperson for the Animal Health Institute, a trade group of animal-drug manufacturers. Cutting drug use on the farm will lead to sicker animals and more potentially dangerous microbes in the food supply. The FDA disagrees, says Linda Tollefson, deputy director of the agency's Center for Veterinary Medicine. Already, the FDA has proposed pulling one class of drugs from the market and tightening rules for others, she says--a proposal industry groups are fighting.
Information on antimicrobial use in animals from the FDA's Center for Veterinary Medicine
Background from the Alliance for the Prudent Use of Antibiotics
Fact sheet from the Animal Health Institute, a trade group of animal-drug producers
Background from the Consumer's Union, an advocacy group