CHICAGO--Researchers have long warned that using antibiotics in livestock could breed drug-resistant bacteria that infect people. Now, a study has confirmed this and pointed to an easy solution: Banning the use of a drug called avoparcin on farms dramatically cut microbe's resistance to a related drug, vancomycin, in Belgian hospital patients. The findings were presented here 17 December at the Interscience Conference on Antimicrobial Agents and Chemotherapy.
European farmers added avoparcin to the feed of chickens and hogs to prevent infections and fatten the animals on less feed, until the European Union banned this use in 1997. That's because physicians need the antibiotic vancomycin, which is chemically similar to avoparcin, to treat potentially deadly infections of bacteria called enterococci that normally live in the human gut. Researchers worried that drug-resistant gut microbes from chickens and hogs would contaminate meat and take up residence in the human gut (Science, 5 May 2000, p. 792). Researchers knew that vancomycin-resistant enteroccoci became scarce in supermarket chicken meat after the ban. But they didn't know if this drop in resistance affected people.
To find out, microbiologist Greet Ieven of the University of Antwerp and her colleagues cultured enterococci from stool samples of 353 hospital patients in May and June 2001 and tested to see how many survived high levels of vancomycin. Just three of the enterococci cultures, or 0.6%, resisted vancomycin--a big drop from the 5.7% resistance rate in 1996, when avoparcin was still widely fed to livestock. Molecular genetic analysis confirmed that the prevalence of a key vancomycin resistance gene plummeted from 5.7% to 0.8%. Because vancomycin is used just as widely in Belgian hospitals now as 5 years ago, the results suggest that vancomycin resistance in human enterococcal infections originated largely on farms, Ieven says.
The results "confirm what people thought might happen in the clinic," agrees pharmacologist Michael Dudley of Microcide Pharmaceuticals in Mountain View, California. Combined with earlier results, the findings mean that antibiotic resistance flows like water from farms to clinics, he says, so by stopping the use of avoparcin, "you stop the tap."
Fact sheet on antibiotic use in animals from the Alliance for the Prudent Use of Antibiotics
Dueling fact sheet from the Animal Health Institute,
a trade group representing makers of animal antibiotics
Editorial on eliminating antibiotics from animal feed