Chicken litter promotes resistance.

• Position: Antibiotics

Researchers may need to take a hard leek at what appear to be certain myths concerning the spread of antibiotic-resistant genes, according to a study by scientists at the University of Georgia, Athens. They found that poultry litter--a ubiquitous part of large broiler operations--harbors a vastly greater number of microbial agents that collect and express resistance genes than was previously thought. Apparently, waste left behind by flocks raised in industrial chicken houses is rich in genes called integrons that promote the spread and persistence of such clusters.

This is a serious and growing problem for farm animal operations and human health. Antibiotic use in treating disease and increasing feed efficiency has been a common part of, industrial farms for more than half a century. When antibiotic-resistant bacteria began to show up in hospitals in the 1950s, researchers initially believed that simply restricting the use of antibiotics on farms could reduce their prevalence among humans, but it has not been that easy.

"Over the past 30 years, we have learned this hope was unrealistic because we share both pathogenic and benign bacteria with other humans and animals, and because bacteria transfer genes among themselves," says microbiologist Anne Summers.

At the heart of the dilemma are integrons, which scientist--until now--have studied exclusively in such pathogenic bacteria as Salmonella and E. coli. The researchers wondered, however: Does the poultry production environment also harbor integrons that assemble these large groups of distinct genes? To find out, they collected samples of poultry litter from broiler houses...