Hwang, Hae Jin2020-09-082020-09-082019-06https://hdl.handle.net/11299/216141University of Minnesota Ph.D. dissertation.June 2019. Major: Environmental Health. Advisors: Randall Singer, George Maldonado. 1 computer file (PDF); viii, 212 pages.Campylobacteriosis, predominantly caused by Campylobacter jejuni, is a common, yet serious foodborne illness. With consumption and handling of poultry products as the most important risk factor of campylobacteriosis, reducing Campylobacter contamination in poultry products is considered the best public health intervention to reduce the burden and costs associated with campylobacteriosis. To this end, there is a need to improve our understanding of epidemiology and ecology of Campylobacter jejuni in poultry. The overall goal of this dissertation is to answer knowledge gaps regarding Campylobacter ecology and epidemiology in broiler chickens with an emphasis on the pre-harvest components of the broiler production system. The objectives included: (1) to assess current interventions and control measures practiced by the U.S. broiler industry to reduce Campylobacter contamination on broiler chicken products; (2) to investigate indirect selective pressures responsible for the persistence of fluoroquinolone-resistant Campylobacter jejuni in broiler chickens; and (3) to describe the temporal changes in broiler litter bacterial microbiota with respect to bird age, flock cycle, antibiotic use and presence of Campylobacter on farms. For the first objective, we surveyed key stakeholders of the U.S. broiler industry, including poultry veterinarians, farm managers and processing plant managers. The survey respondents reported the use of various pre- and post-harvest interventions that are recommended by the USDA-FSIS to decrease Campylobacter contamination in broiler chickens and on carcasses. Yet, the survey results also revealed the lack of understanding of Campylobacter epidemiology among the respondents, indicating that further education and training programs are necessary to improve understanding of Campylobacter among the key stakeholders which can lead to a reduction of Campylobacter contamination and improvement in food safety. To investigate indirect selective pressures allowing persistence of Campylobacter jejuni in broiler chickens, we tested two hypotheses: limited bioavailability in poultry and activity of microcin B17. However, we found that the hypotheses tested were unlikely to be responsible for the persistence of fluoroquinolone-resistant Campylobacter jejuni despite the lack of fluoroquinolone use in the industry. Lastly, we investigated the temporal changes in the broiler litter microbiota by sampling seven commercial broiler farms over two flock cycles. We found that flock cycle and age of bird were two significant farm variables driving the bacterial diversity and composition of the litter microbiota. Additionally, when the litter bacterial microbiota was compared between Campylobacter-positive and Campylobacter-negative samples, a lower abundance of Lactobacillus was observed among the positive samples. Overall, the work presented in this dissertation demonstrates collective efforts to improve our understanding of Campylobacter jejuni in broiler chickens using multidisciplinary approaches.enCampylobacter jejuniFood SafetyPoultryThesis or Dissertation