Impact of Intestinal Antibiotic Concentration On The Microbiota and Antimicrobial Susceptibility of Foodborne Pathogens in Cattle

The long-term goal of our research program is to develop rational, research-based recommendations for food animal veterinarians to maximize antibiotic efficacy while minimizing risk of antimicrobial resistance (AMR). The objective of this proposal is to determine the GIT concentrations of the fluoroquinolone danofloxacin and macrolide tulathromycin, their impact on the microbiota and foodborne pathogens, and the persistence of these changes. These findings would drive the development of a "microbiological withdrawal time." These twodrugs represent antibiotic classes widely used in veterinary medicine and human medicine that exhibit links to AMR in zoonotic pathogens. Based on preliminary data with enrofloxacin presented below, the central hypothesis for this proposal is that danofloxacin will cause significant, but short-lived changes to the gut microbiota, while tulathromycin will produce more long lasting changes due to its slow elimination and concentration in tissues. Measuring
changes to the microbiota and fecal pathogens over time willallow us to calculate a "microbiological withdrawal time," which would be the time until the fecal concentration of AMR pathogens drops below a safe threshold. This will provide an easily implemented, scientifically-justified recommendation to mitigate emergence and spread of AMR foodborne pathogens.