A team of University of Georgia scientists suggest that curbing the use of antimicrobials on poultry farms will do little to reduce rates of infection with antimicrobial-resistant bacteria that have the potential to threaten human health.

Dr. Margie Lee, professor at the UGA College of Veterinary Medicine, and her colleagues have found that chickens raised on antimicrobial-free farms, and even those raised under pristine laboratory conditions, have high concentrations of bacteria that are resistant to common antimicrobials. Her findings, published in the March issue of the journal Applied and Environmental Microbiology, suggest that poultry come to the farm harboring resistant bacteria, possibly acquired as they were developing in their eggs.

The study was funded by grants from the Food and Drug Administration and the Department of Agriculture.

"This issue of antibiotic resistance is more complicated than once thought," Dr. Lee said. "These findings suggest that banning antibiotics at the farm level may not be as effective as assumed. We need further studies to identify which management practice would be effective."

The concern over the emergence of microbes resistant to antimicrobials that are used to treat human and animal infections led the European Union to ban the marketing and use of antimicrobials as growth promoters in animal feed. The final step in the phaseout was completed in January 2006.

In the United States, the Food and Drug Administration announced in July 2005 that it would ban the distribution or use of the antimicrobial enrofloxacin for poultry, which was marketed by Bayer Corporation under the name Baytril 3.23% Concentrate Antimicrobial Solution. The FDA said enrofloxacin caused resistance in Campylobacter jejuni when used to treat respiratory infections in poultry.

"They banned Baytril in 2005, and if you look at Baytril resistance in Campylobacter now, it's essentially unchanged," Dr. Lee said.

Currently, Congress is considering legislation to reduce routine use of antimicrobials in animal agriculture. The Preservation of Antibiotics for Medical Treatment Act (S. 549/H.R. 962) would phase out the use of certain antimicrobial drugs in food-producing animals for nontherapeutic purposes such as growth promotion, feed efficiency, weight gain, routine disease prevention, and other routine uses. Turn to page 976 in the April 1 issue of JAVMA News to learn why the AVMA has not supported passage of the legislation in the past.