Antibiotic use in conventional animal food production in the United States has created public health concern because it has been shown to contribute to the development of antibiotic-resistant bacteria that can potentially spread to humans. A new study, led by Dr. Amy R. Sapkota of the University of Maryland School of Public Health, provides data demonstrating that poultry farms that have transitioned from conventional to organic practices and ceased using antibiotics have significantly lower levels of drug-resistant enterococci bacteria. The study, published in Environmental Health Perspectives (online August 10, 2011), is the first to demonstrate lower levels of drug-resistant bacteria on newly organic farms in the United States and suggests that removing antibiotic use from large-scale U.S. poultry farms can result in immediate and significant reductions in antibiotic resistance for some bacteria.
"We initially hypothesized that we would see some differences in on-farm levels of antibiotic-resistant enterococci when poultry farms transitioned to organic practices. But we were surprised to see that the differences were so significant across several different classes of antibiotics even in the very first flock that was produced after the transition to organic standards," explains Sapkota, an Assistant Professor with the Maryland Institute for Applied Environmental Health. "It is very encouraging."
Sapkota and her team, which included R. Michael Hulet (Pennsylvania State University), Guangyu Zhang, Sam Joseph and Erinna Kinney (University of Maryland), and Kellogg J. Schwab (Johns Hopkins Bloomberg School of Public Health), investigated the impact of removing antibiotics from U.S. poultry farms by studying ten conventional and ten newly organic large-scale poultry houses in the mid-Atlantic region. They tested for the presence of enterococci bacteria in poultry litter, feed, and water, and tested its resistance to 17 common antimicrobials.
"We chose to study enterococci because these microorganisms are found in all poultry, including poultry on both organic and conventional farms. The enterococci are also notable opportunistic pathogens in human patients staying in hospitals. In addition, many of the antibiotics given in feed to farm animals are active against Gram-positive bacteria such as the enterococci. These features, along with their reputation of easily exchanging resistance genes with other bacteria, make enterococci a good model for studying the impact of changes in antibiotic use on farms," Sapkota explains.