Submitted to: Frontiers in Microbiology
Publication Type: Peer reviewed journal
Publication Acceptance Date: 5/20/2014
Publication Date: 6/10/2014
Citation: Looft, T.P., Allen, H.K., Casey, T., Alt, D.P., Stanton, T.B. 2014. Carbadox has both temporary and lasting effects on the swine gut microbiota. Frontiers in Microbiology. DOI: 10.3389/fmicb.2014.00276. Interpretive Summary: The use of antibiotics in agriculture to treat and prevent animal disease and to promote growth is a growing concern because of the potential of increasing antibiotic resistant bacteria entering the food supply and compromising treatment of human disease. Defining the effects of antibiotics on intestinal bacteria in food animals will help in the search for alternatives with similar desirable effects on animal growth without causing more antibiotic resistant bacteria that might cause human disease. In this study we found that a popular antibiotic added to pig feed to treat dysentery and promote growth, caused the types of bacteria to change quickly after feeding pigs the antibiotic. Some bacteria higher in the pigs receiving antibiotics are associated with healthy animals and may be responsible for the performance benefits seen when antibiotics are fed to pigs. Many of these differences were lost after the first week, suggesting that the effects were strongest in the beginning. After switching all pigs to a different non-antibiotic containing diet, Escherichia coli bacteria increased in the pigs that had never received the antibiotic, but not in those that had been fed the antibiotic. This suggests that the antibiotic prevented an increase of E. coli, even after the antibiotic was removed. We also showed the antibiotic didn’t impact all bacteria equally, with many decreasing while a small number remained unchanged. This work is an important first step for finding alternatives to antibiotics and promoting growth of animals for food by encouraging beneficial bacteria. These studies also contribute useful information for veterinarians and food animal producers seeking to improve food safety and animal production.
Technical Abstract: Antibiotics are used in livestock and poultry production to treat and prevent disease as well as to promote animal growth. Carbadox is an in-feed antibiotic that is widely used in swine production to prevent dysentery and to improve feed efficiency. The goal of this study was to characterize the effects of carbadox and its withdrawal on the swine gut microbiota. Six pigs (initially three weeks old) received feed containing carbadox and six received unamended feed. After three weeks of continuous carbadox administration, all pigs were switched onto a maintenance diet without carbadox. DNA was extracted from fecal samples (n=142) taken before, during, and following (6 week withdrawal) carbadox treatment. Phylotype analysis using 16S rRNA sequences isolated from fecal samples showed the gradual development of the non-medicated swine gut microbiota over the 8-week study and that the carbadox-treated pigs had significant differences in bacterial membership relative to non-medicated pigs. Enumeration of fecal Escherichia coli (E. coli) showed that a diet change concurrent with carbadox withdrawal was associated with a significant increase in the E. coli in the non-medicated pigs, suggesting that carbadox pretreatment prevented an increase of E. coli populations. In-feed carbadox caused striking effects within four days of administration, with significant alterations in both community structure and bacterial membership, notably a large relative increase in Prevotella populations in medicated pigs. The increase detected in the phylotype analysis, was contradicted by digital PCR that showed the absolute abundance of Prevotella was unchanged between the medicated and non-medicated pigs. Carbadox therefore caused a decrease in the abundance of other gut bacteria. The pending regulation on antibiotics used in animal production, underscores the importance of understanding how they modulate the microbiota, impact animal health, and thereby inform the search for antibiotic alternatives.