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Antimicrobial resistance surveillance in feedlot cattle




Benedict, Katharine M., author
Morley, Paul S., advisor
Booker, Calvin W., committee member
Van Metre, David C., committee member
Basaraba, Randall J., committee member

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Objectives: To develop and validate methodological components of a model for surveillance of antimicrobial use and resistance in feedlot cattle. Methods: A web-based survey of participants knowledgeable and interested in antimicrobial use in beef feedlots was used to solicit responses regarding appropriate metrics for quantifying, analyzing, and reporting antimicrobial exposures. The accuracies of two susceptibility tests commonly recommended for surveillance programs were determined using stochastic latent class analysis. Multivariable logistic and linear regression was used to investigate associations between exposures to antimicrobial drugs and antimicrobial resistance. Results: When reporting antimicrobial use in the context of antimicrobial resistance, survey participants believed that the Animal Defined Daily Dose metric was the most accurate. The two susceptibility tests investigated had comparable accuracies for the antimicrobial drugs tested. Exposure to parenteral tetracycline in the study feedlots was associated with resistance to tetracycline; however, exposures to all other classes of antimicrobials were not associated with antimicrobial resistance. Conclusions: Appropriate metrics for reporting and analyzing antimicrobial resistance are necessary to accurately investigate associations between use and resistance, though clarity of what the metric represents may be lost. Testing of susceptibility in surveillance programs is equally valid by way of disk diffusion testing. Multivariable logistic regression was an appropriate and useful method to investigate associations between use and resistance. Parenteral exposures to antimicrobials did not drive antimicrobial resistance at mid-feeding period.


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