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1. Denholm, Rachael Ann. Changes in Antimicrobial Resistance from 1994 to 2011 and Exploring Farm Management Practices Associated with Antimicrobial Resistance in Salmonella on U.S. Beef Feedlots.

Degree: MPH, Public Health, 2017, The Ohio State University

Antimicrobial resistance (AMR) is a growing concern in human and animal medicine and threatens public health on a global scale. Beef cattle are a reservoir of Salmonella and have been implicated in foodborne outbreaks of AMR Salmonella in the U.S. Understanding trends in AMR and factors which affect resistance to medically important antibiotics in beef cattle is vital to animal and human health. The USDA’s National Animal Health Monitoring System administered farm management questionnaires to beef feedlots in major cattle-feeding states around the U.S. and collected fecal samples from 100 feedlots in 1994, 73 feedlots in 1999, and 68 feedlots in 2011 for pathogen and AMR testing. The objectives of this study were to 1) evaluate change in the prevalence of AMR in Salmonella over time from USDA beef feedlot studies conducted in 1994, 1999, and 2011 and 2) to explore farm management factors, including antibiotic use, associated with the odds of AMR in a Salmonella isolate. Logistic regression models were created for each of four antibiotics: amoxicillin-clavulanic acid, ampicillin, ceftiofur, and trimethoprim-sulfamethoxazole. Final models were selected via backward elimination to measure statistical associations between management factors and odds of a Salmonella isolate being resistant to the antibiotic. There was a significant increase in odds of resistance from 1994 to 1999 for all four antibiotics, amoxicillin-clavulanic acid (OR=32.6), ampicillin (OR=6.1), ceftiofur (OR=115.4), and trimethoprim-sulfamethoxazole (OR=17.4). Isolates from 1999 had significantly higher odds of resistance compared with isolates from 2011 for amoxicillin-clavulanic acid (OR=3.8) and trimethoprim-sulfamethoxazole (OR=35.0). Use of antibiotics tylosin, tetracyclines, and sulfas as health or production management tools did not approach significance (p=0.20) in any of the four models. Management practices associated with increased odds of resistance to at least one antimicrobial included: use of environmental spray for fly control; use of fly traps or sticky tape for fly control; having more than 10% dairy breed animals; use of a private veterinarian who makes regular visits; larger herds. Management practices associated with decreased odds of resistance to at least one antimicrobial included: feeding tallow in the preceding seven days; disposing of a higher percentage of manure on the feedlot’s land. The AMR increase throughout the 1990s coincided with emergence of the Salmonella Newport AmpC gene, and the slight decrease through the 2000s parallels NARMS reports of decrease in resistance conferred by the AmpC gene in human isolates. Knowledge of trends in resistance to particular antibiotics can help inform policy and outbreaks of AMR foodborne pathogens. This study can be used to generate hypotheses for future research of potential risk factors for AMR to continue investigating on-farm interventions for reduction of AMR Salmonella. Advisors/Committee Members: Habing, Gregory (Advisor).

Subjects/Keywords: Animal Diseases; Public Health; Agriculture; Veterinary Services; Statistics; antimicrobial resistance; antibiotic resistance; salmonella; beef; feedlot; USDA; cattle health; animal health; farm management; antibiotic use; resistance; trends; NAHMS; public health; foodborne; pathogens; food safety

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APA (6th Edition):

Denholm, R. A. (2017). Changes in Antimicrobial Resistance from 1994 to 2011 and Exploring Farm Management Practices Associated with Antimicrobial Resistance in Salmonella on U.S. Beef Feedlots. (Masters Thesis). The Ohio State University. Retrieved from http://rave.ohiolink.edu/etdc/view?acc_num=osu1492702064126336

Chicago Manual of Style (16th Edition):

Denholm, Rachael Ann. “Changes in Antimicrobial Resistance from 1994 to 2011 and Exploring Farm Management Practices Associated with Antimicrobial Resistance in Salmonella on U.S. Beef Feedlots.” 2017. Masters Thesis, The Ohio State University. Accessed September 20, 2017. http://rave.ohiolink.edu/etdc/view?acc_num=osu1492702064126336.

MLA Handbook (7th Edition):

Denholm, Rachael Ann. “Changes in Antimicrobial Resistance from 1994 to 2011 and Exploring Farm Management Practices Associated with Antimicrobial Resistance in Salmonella on U.S. Beef Feedlots.” 2017. Web. 20 Sep 2017.

Vancouver:

Denholm RA. Changes in Antimicrobial Resistance from 1994 to 2011 and Exploring Farm Management Practices Associated with Antimicrobial Resistance in Salmonella on U.S. Beef Feedlots. [Internet] [Masters thesis]. The Ohio State University; 2017. [cited 2017 Sep 20]. Available from: http://rave.ohiolink.edu/etdc/view?acc_num=osu1492702064126336.

Council of Science Editors:

Denholm RA. Changes in Antimicrobial Resistance from 1994 to 2011 and Exploring Farm Management Practices Associated with Antimicrobial Resistance in Salmonella on U.S. Beef Feedlots. [Masters Thesis]. The Ohio State University; 2017. Available from: http://rave.ohiolink.edu/etdc/view?acc_num=osu1492702064126336

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