Degree Type


Date of Award


Degree Name

Doctor of Philosophy


Veterinary Microbiology and Preventive Medicine


Veterinary Microbiology

First Advisor

Qijing Zhang


Ruminant Campylobacter, (C. jejuni and C. coli), contributes significantly to foodborne illnesses in humans. A recently emerged C. jejuni clone (named SA) is also a major cause of ruminant abortion in the United States. Despite the importance of Campylobacter in ruminant health and food safety, little is known about its prevalence and antibiotic resistance profiles in cattle production systems in the U.S. In this project, we examined the antibiotic resistance susceptibility and mechanisms of the Campylobacter isolates derived from 35 feedlot cattle farms in 5 different states, and determined the distribution of C. jejuni clone SA in the feedlots and in dairy cows by using isolates collected by NAHMS Dairy Studies 2002, 2007 and 2014. In feedlot cattle, clone SA accounted for 5.8% of the total C. jejuni isolates, but prevalence varied from farm to farm. In dairy cattle, the overall prevalence of clone SA was 7.2%, and a declining trend in the prevalence was detected from 2002 to 2014. Whole genome sequence analyses of the dairy isolates revealed the high genomic stability of clone SA over the years. The results also revealed high prevalence of fluoroquinolone (FQ) resistance in the feedlot cattle isolates. Molecular typing revealed that clonal expansion was involved in dissemination of FQ-resistant C. coli. Notably, florfenicol resistance, which was historically low in Campylobacter, also emerged in the bovine Campylobacter isolates. Whole genome sequencing analysis identified a novel cfr variant, named cfr(C), in the florfenicol-resistant isolates. Cloning of cfr (C) and conjugative transfer of the cfr (C)-containing plasmid confirmed its role in conferring resistance to multiple classes of antibiotics including phenicols, lincosamides, pleuromutilins, and oxazolidinones. The cfr(C) gene was detected in 10% of the C. coli isolates, and molecular typing revealed its spread mainly via clonal expansion. These findings reveal the common presence of C. jejuni clone SA in both beef and dairy cattle and the rising prevalence of FQ-resistant Campylobacter as well as the emergence of a novel multidrug resistant mechanism Cfr(C) in ruminant Campylobacter in the U.S. These results provide new insights into the epidemiology and antibiotic resistance of Campylobacter in the bovine reservoir.

Copyright Owner

Yizhi Tang



File Format


File Size

125 pages

Included in

Microbiology Commons