High Prevalence of Fluoroquinolone-Resistant Bacteria in Sheep and Increased Counts in the Bile and Gallbladders of Sheep Medicated with Tetracycline in Feed.

is a major foodborne pathogen in humans and a significant cause of abortion in sheep. Although ruminants are increasingly recognized as important reservoirs for species, limited information is available about the molecular epidemiology and antimicrobial resistance (AMR) profiles of sheep Here, we describe a two-trial study that examined profiles in sheep and determined whether in-feed tetracycline (TET) influenced the distribution and AMR profiles of Each trial involved 80 commercial sheep naturally infected with : 40 of these sheep were medicated with tetracycline in feed, while the other 40 received feed without antibiotics. Fecal and bile samples were collected for the isolation of The bacterial isolates were analyzed for antimicrobial susceptibility and genotypes. The results revealed that 87.0% and 61.3% of the fecal and bile samples were positive for ( and ), with no significant differences between the medicated and nonmedicated groups. All but one of the tested isolates were resistant to tetracycline. Although fluoroquinolone (FQ) resistance remained low in (1.7%), 95.0% of the isolates were resistant to FQ. Genotyping revealed that sequence type 2862 (ST2862) and ST902 were the predominant genotypes in the sheep. Feed medication with tetracycline did not affect the overall prevalence, species distribution, and AMR profiles of , but it did increase the total counts in bile and gallbladder. These findings identify predominant clones, reveal the high prevalence of FQ-resistant , and provide new insights into the epidemiology of in sheep. is a major cause of foodborne illness in humans, and antibiotic-resistant is considered a serious threat to public health in the United States and worldwide. As a foodborne pathogen, commonly exists in the intestinal tract of ruminant animals, such as sheep and cattle. Results from this study reveal the predominant genotypes and high prevalence of tetracycline (TET) and fluoroquinolone (FQ) resistance in sheep The finding on fluoroquinolone resistance in sheep is unexpected, as this class of antibiotics is not used for sheep in the United States, and it may suggest the transmission of fluoroquinolone-resistant from cattle to sheep. Additionally, the results demonstrate that in-feed medication with tetracycline increases counts in gallbladders, suggesting that the antibiotic promotes colonization of the gallbladder. These findings provide new information on epidemiology in sheep, which may be useful for curbing the spread of antibiotic-resistant in animal reservoirs.