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.