Antibiotics in pig feed increased the number of antibiotic-resistant genes in gastrointestinal microbes in pigs, according to a study conducted by Michigan State University and the U.S. Department of Agriculture’s Agricultural Research Service.
Published in the Proceedings of the National Academy of Sciences, the study focused on understanding the effects of conventional, in-feed antibiotics in U.S. farms. “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,” said Torey Looft, USDA researcher.
Additional findings included:
- 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, according to the researchers.
- 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, said the researchers.