Degree Type


Date of Award


Degree Name

Doctor of Philosophy


Veterinary Microbiology and Preventive Medicine

First Advisor

Thaddeus Stanton

Second Advisor

Gwyn Beattie


After sixty years on antibiotic use in livestock production, antimicrobial resistance is an issue that cannot be ignored. While governments debate new regulations, evidence is accumulating that in-feed antibiotics are contributing to antibiotic resistance proliferation in intestinal microbes and potential pathogens. The mode of action for the growth benefits of antibiotics are not clear, but defining the intestinal bacterial communities and understanding the impact of antibiotics on it is an important link in developing viable alternatives to antibiotics. Identifying the members and functions within the bacterial communities is needed to identify niches within the intestinal tract. Here we evaluate the shifts in intestinal bacterial communities with in-feed antibiotics, which include membership and functional changes. Additionally, antibiotic-resistance genes increased in the intestinal communities after exposure to antibiotics. To evaluate localize adaptations of swine intestinal bacterial communities; the spatial distribution of bacterial communities was evaluated. Localized differences were detected and potential specialist such as mucin degraders were identified. Future research will need to direct therapies to mimic the beneficial effects of antibiotics on the host and gut bacteria while minimizing the collateral impact on health and safety.


Copyright Owner

Torey P. Looft



Date Available


File Format


File Size

194 pages