(Beyond Pesticides, August 15, 2011) Poultry farms that have adopted organic practices and cease using antibiotics have significantly lower levels of drug-resistant enterococci bacteria that can potentially spread to humans, according to a new study published August 10, 2011 in the online edition of Environmental Health Perspectives. The study, led by researchers at the University of Marylandâ€™s School of Public Health, suggests that organic conversion of U.S. poultry farms can result in immediate and significant reductions in antibiotic resistance for some bacteria.
The non-therapeutic use of antibiotics in livestock production accounts for nearly 80% of all antibiotics used in the United States. Typically, low levels of antibiotics are administered to animals through feed and water to prevent disease and promote growth. This is generally done to compensate for overcrowded and unsanitary living conditions, as is common in concentrated animal feeding operations (CAFOs), and to fatten livestock to get them to market sooner. Antibiotic use is prohibited in the production of all animal products labeled organic.
“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,” explained Amy Sapkota, PhD, an assistant professor with the Maryland Institute for Applied Environmental Health. “It is very encouraging.”
Dr. Sapkota and her team investigated the impact of removing antibiotics from U.S. poultry farms by studying 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,” Dr. Sapkota said.
While all farms tested positive for the presence of enterococci in poultry litter, feed, and water as expected, the newly organic farms were characterized by a significantly lower prevalence of antibiotic-resistant enterococci. For example, 67 percent of Enterococcus faecalis recovered from conventional poultry farms were resistant to erythromycin, while 18 percent of Enterococcus faecalis from newly organic poultry farms were resistant to this antibiotic.
Dramatic changes were also observed in the levels of multi-drug resistant bacteria (organisms resistant to three or more antimicrobial classes) on the newly 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 [see figure].
“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, said Dr. Sapkota. â€śNow we need to look forward and see what happens over five years, 10 years in time.” Sapkota said she expects that reductions in drug-resistant bacteria on U.S. farms that “go organic” are likely to be more dramatic over time as reservoirs of resistant bacteria in the farm environment diminish.
Last November, the University of Georgiaâ€™s Center for Food Safety released a similarstudy that documents the comparative rates of salmonella contamination in both feces and feed at organic and conventional broiler poultry farms in North Carolina. There were three organic and four conventional farms included in the study, all owned by the same company. The researchers found that, in examining fecal samples, 38.8% of those from conventional farms contained salmonella, compared with only 5.6% from organic farms. For feed, the results were similar: 27.5% of feed on the conventional farms had salmonella, while only 5% of organic feed was contaminated. The study also examined the prevalence of salmonella that are resistant to antibiotic treatment and compared the results of organic versus conventional. The results show that resistance to the antibiotic streptomycin is 36.2% at conventional farms, compared to 25% at organic. Perhaps even more significant, multi-drug resistance to six different antibiotic treatments (ampicillin, streptomycin, amoxicillin, cephalothin, ceftiofor, and cefoxitin) is at 39.7% on the conventional farms, whereas none of the organic birds show resistance to this combined treatment.
In May 2011, a coalition of environmental and public health groups filed a lawsuit against the federal Food and Drug Administration (FDA) to require the agency to enforce strict standards regarding the routine use of antibiotics in livestock feed. The suit, filed by the Natural Resources Defense Council, the Center for Science in the Public Interest, Food Animal Concerns Trust, Public Citizen, and the Union of Concerned Scientists, calls on FDA to implement regulations based on its own findings that the routine use of low doses of antibiotics in animal feed presents increased risk for the development of resistant bacteria.
Antibiotic and antimicrobial resistance is a serious public health issue, since it can lead to infections that are difficult or impossible to treat. When they are used in small doses, such as in livestock feed or antimicrobial hand soaps containing triclosan, the drugs kill a small amount of the microbial population, but the ones that survive evolve immunity to the treatment and pass this on to future generations. These resistant populations can then grow and eventually come in contact with humans, putting the general public at risk of untreatable infection.
To learn more about the benefits of organic agriculture, see Beyond Pesticide’s organic program page.