Genetic Mechanisms Contributing to Reduced Tetracycline Susceptibility of Campylobacter Isolated from Organic and Conventional Dairy Farms in the Midwestern and Northeastern United States
Abstract:Campylobacter is one of the most common causes of gastroenteritis and can be acquired through contact with farm animals or the consumption of raw milk. Because of concerns over the role of food-producing animals in the dissemination of antimicrobial resistance to humans, we evaluated the prevalence of antimicrobial resistance in Campylobacter isolates from dairy farms and the genetic mechanism conferring the observed resistance. Evaluation of antimicrobial resistance was completed on 912 isolates from conventional and 304 isolates from organic dairy farms to eight drugs (azithromycin, chloramphenicol, ciprofloxacin, clindamycin, erythromycin, gentamicin, nalidixic acid, and tetracycline) with microbroth dilution. Resistance to seven of eight drugs was very low and did not differ by farm type. However, tetracycline resistance was common in Campylobacter isolated from both organic and conventional dairy farms, with 48 and 58% of isolates affected, respectively. By multiplex PCR, we determined that tetracycline resistance was highly associated with the carriage of tetO in Campylobacter isolates (χ2 = 124, P < 0.01, kappa = 0.86).
Document Type: Research Article
Affiliations: 1: Population Medicine Center, Michigan State University, East Lansing, Michigan 48824, USA; U.S. Drug Safety, P?zer Animal Health, Exton, PA 19520, USA 2: Population Medicine Center, Michigan State University, East Lansing, Michigan 48824, USA 3: College of Veterinary Medicine, Michigan State University, East Lansing, Michigan 48824, USA 4: College of Agriculture and Life Sciences, University of Wisconsin, Madison, Wisconsin 53706, USA 5: College of Veterinary Medicine, Cornell University, Ithaca, New York 14853, USA 6: College of Veterinary Medicine, University of Minnesota, St. Paul, Minnesota 55108, USA 7: College of Veterinary Medicine, University of Minnesota, St. Paul, Minnesota 55108, USA; Centers for Epidemiology and Animal Health, USDA-APHIS-VS, Fort Collins, CO 80562, USA