The fast-food chain McDonald’s announced on June 19 that it will stop its farms under contract from feeding chicken, cattle, and pigs certain antibiotics intended to accelerate the animals’ growth. That step might slow or reverse the rise of antibiotic-resistant bacteria that can infect people, scientists say.
“I’m delighted,” says Stuart B. Levy of the Tufts University School of Medicine in Boston. “This move by McDonald’s . . . puts a stamp of credibility” on the idea that antibiotics are not needed to promote growth in farm animals, he says. “I expect other companies will follow suit.”
McDonald’s new policy calls for producers that sell meat only to McDonald’s to phase out by the end of 2004 their use of antibiotics belonging to classes that contain any drugs used in medicine. Most of the chicken served in McDonald’s restaurants worldwide comes from companies that sell exclusively to the chain, but most of the company’s beef and pork come from nonexclusive suppliers.
The fast-food company will offer incentives for nonexclusive suppliers to reduce their use of antibiotics, the company said. The new policy is the product of a yearlong review that included input from environmental groups and companies that grow livestock.
Farms that sell to McDonald’s may continue to use antibiotics to treat sick animals and to prevent illness in animals that may have been exposed to infections. Producers may also continue to use antibiotics that don’t belong to the classes now restricted by McDonald’s.
An unknown but substantial fraction of all antibiotics used in the United States is administered to healthy livestock rather than to sick animals or people. Livestock farmers decades ago concluded that feeding growing animals small, regular doses of antibiotics accelerates the animals’ weight gain and reduces the costs of producing meat.
Researchers have tied the use of antibiotic growth promoters in livestock to increased risk of antibiotic-resistant infections in people (SN: 10/20/01, p. 246: http://sciencenews.org/20011020/fob5.asp) and suspect that such use of the drugs hastens the end of their medical effectiveness (SN: 4/27/02, p. 259: Available to subscribers at http://sciencenews.org/20020427/fob1.asp). Any extensive use of antibiotics can encourage the proliferation of some nasty bacteria because the drug allows only drug-resistant microbes to survive. Consequently, various scientific and consumer organizations have called on livestock producers and meat sellers to reduce the use of antibiotic growth promoters.
Assuming that companies and farms selling meat to McDonald’s reduce their use of antibiotics in response to the company’s decision, “we could expect, but not be assured of, a reduction over 3 or 4 years in the prevalence of resistance to those drugs,” says Marc Lipsitch of the Harvard School of Public Health in Boston.
Scientists in Denmark observed such a fall in antibiotic-resistant bacteria during the late 1990s, after the country banned the use of antibiotics as animal-growth promoters (SN: 8/5/00, p. 95: Available to subscribers at http://sciencenews.org/20000805/note17.asp). The European Union has since banned all antibiotics as animal-growth promoters.
However, Lipsitch says that if livestock producers simply switch from antibiotics in the classes that McDonald’s won’t buy to growth promoters from other classes of antibiotics, bacterial drug resistance might remain at its current prevalence or continue to increase. That’s because the genes that give bacteria resistance to antibiotics often cluster on bits of genetic material called plasmids. If a single plasmid contains at least two genes that confer resistance to different antibiotics, then evolutionary pressures favoring resistance to one drug will increase resistance to another.
Lipsitch also notes that antibiotics currently used in agriculture but not in medicine may eventually be used in people. If bacterial resistance to those drugs is already high because of their use as animal-growth promoters, they could have limited effectiveness as infection fighters in people, he says.
Limiting the use of antibiotics for animal-growth promotion is an important step toward reducing bacterial resistance to medical drugs, says Levy, but he emphasizes that doctors also must be more prudent in prescribing antibiotics if medicine is going to combat growing drug resistance in microbes.