Antibiotics in pig feed increased the number of antibiotic resistant genes in gastrointestinal microbes in pigs, according to a study by Michigan State University and USDA’s Agricultural Research Service (ARS). But researchers point out that longer term studies are needed to learn more specifics.

“To our knowledge, this study is the first of its kind to look at the collateral impacts of in-feed antibiotic use in farm animals, using a comprehensive approach to detect shifts in the function and the makeup or membership of the microbial community in the model animal’s gastrointestinal tract,” says Torey Looft, USDA researcher.

Published in the current edition of the Proceedings of the National Academy of Sciences, the study focused on understanding the effects of conventional, in-feed antibiotics in U.S. farms.

Producers of pigs, chickens and other farm animals use antibiotics in a variety of ways, including for disease treatment and prevention. Some of the in-feed benefits include enhancing the animals’ growth rates, feed efficiency and weight gain.

Scientists don’t know precisely how antibiotics enhance growth rates and feed efficiency, but there is concern that on-farm use of these medications may contribute to the development of microbe strains that are resistant to conventional antibiotics, which are potentially harmful to humans and animals, says James Tiedje, Michigan State distinguished professor of microbiology and molecular genetics and of crop and soil sciences.

Still, wide-ranging studies continue to present conflicting results and solid conclusions remain elusive.

“The growth of antibiotic resistance in pathogens is a huge challenge for society around the world,” Tiedje says. “Studies to understand what contributes to the spread and what interventions can help control the problem are vital.”

Among the Michigan States/ARS study’s findings:

  • Both diversity and abundance of antibiotic resistance genes increased in the intestinal microbial communities of the pigs treated with antibiotics. Longer term studies are needed, researchers say.
  • Some of the genes found in the treated pigs were unexpected and usually linked to antibiotics not used in the study.
  • Microbial genes associated with production and use of energy by microbes increased in abundance in the antibiotic-fed pigs, which may shed light on how antibiotics increase livestock growth and feed efficiency.
  • E. coli populations increased in the intestines of the treated pigs. Further study is needed to clarify this observation and what if any impact it has.

Additional Michigan State researchers involved in the study included Tim Johnson, doctoral student; Robert Stedtfeld, civil and environmental engineering research associate; Woo Jun Sul, doctoral student; Tiffany Stedtfeld, civil and environmental engineering technical aide; Benli Chai, information technologist, Center for Microbial Ecology; James Cole, assistant professor at the Center for Microbial Ecology; and Syed Hashsham, civil and environmental engineering professor.

Funding was provided by the university’s Environmental Science and Policy Program initiative on Pharmaceuticals in the Environment, ARS and the National Institutes of Health and through the Alliance for the Prudent Use of Antibiotics program on Reservoirs of Antibiotic Resistance.

Source: Michigan State University