chickens-eating-antibiotics-700.jpgPoultry farms that transition to organic and stop giving their birds antibiotics have significantly lower levels of drug-resistant bacteria, according to new research out of the University of Maryland’s School of Public Health.

The authors of the study, published in Environmental Health Perspectives this week, say it’s the first to demonstrate lower levels of drug-resistant bacteria on newly organic farms in the United States, adding credence to what environmental and public health advocates have been saying for years: antibiotic usage needs to be curtailed in American agriculture to combat growing antibiotic resistance.

Most experts agree that overusing antibiotics in both human medicine and animal agriculture is contributing to the problem — more than 100,000 people in the U.S. die from bacterial infections, 70 percent of which are resistant to antibiotics. Recent U.S. Food and Drug Administration data indicate approximately 80 percent of all antibiotics sold in the U.S. are given to food animals. 

This research, which comes just days after the largest Class I recall of a USDA-regulated product for multi-drug resistant Salmonella Heidelberg, suggests that removing antibiotics from large-scale poultry farms can have an immediate impact lowering antibiotic resistance for some enterococci bacteria, a genus of bacteria that can cause infections in humans.

“We initially thought 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 of birds that was produced after the transition to organic standards,” said Amy Sapkota, an assistant professor with the Maryland Institute for Applied Environmental Health. “It is very encouraging.”

Sapkota and her team, which included researchers from Pennsylvania State University and Johns Hopkins Bloomberg School of Public Health, measured the impact of removing antibiotics from poultry farms by looking at 10 conventional and 10 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 also cause infections in human patients staying in hospitals. In addition, many of the antibiotics given in feed to farm animals are used to fight 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,” explained Sapkota.

As expected, Enterococci bacteria were present in the poultry litter, feed and water at all farms, conventional and organic, but the newly organic farms had a markedly lower percentage of bacteria resistant to commonly used antibiotics.

According to researchers, 67 percent of Enterococcus faecalis recovered from conventional poultry farms were resistant to erythromycin, a drug widely used to treat infection in humans. At the recently transitioned organic farms, 18 percent of Enterococcus faecalis were resistant to the same antibiotic.

“Dramatic” changes were also observed in other multi-drug resistant bacteria — organisms resistant to three or more antimicrobial classes — on the organic farms.

“Multi-drug resistant bacteria are of particular public health concern because they can be resistant to all available antibiotics, and are, therefore, very difficult to treat if contracted by an animal or human. Forty-two percent of Enterococcus faecalis from conventional farms were multi-drug resistant, compared to only 10 percent from newly organic farms, and 84 percent of Enterococcus faecium from conventional farms were multi-drug resistant compared to 17 percent of those from newly organic farms,” the researchers said.

“While we know that the dynamics of antibiotic resistance differ by bacterium and antibiotic, these findings show that, at least in the case of enterococci, we begin to reverse resistance on farms even among the first group of animals that are grown without antibiotics, added Sapkota. “Now we need to look forward and see what happens over five years, 10 years in time.”