Resistance Gene Transfer during Treatments for Experimental Avian Colibacillosis

Abstract

ABSTRACTAn experiment was conducted in animal facilities to compare the impacts of four avian colibacillosis treatments—oxytetracycline (OTC), trimethoprim-sulfadimethoxine (SXT), amoxicillin (AMX), or enrofloxacin (ENR)—on the susceptibility ofEscherichia coliin broiler intestinal tracts. Birds were first orally inoculated with rifampin-resistantE. colistrains bearing plasmid genes conferring resistance to fluoroquinolones (qnr), cephalosporins (blaCTX-MorblaFOX), trimethoprim-sulfonamides, aminoglycosides, or tetracyclines. Feces samples were collected before, during, and after antimicrobial treatments. The susceptibilities ofE. colistrains were studied, and resistance gene transfer was analyzed. An increase in the tetracycline-resistantE. colipopulation was observed only in OTC-treated birds, whereas multiresistantE. coliwas detected in the dominantE. colipopulations of SXT-, AMX-, or ENR-treated birds. Most multiresistantE. colistrains were susceptible to rifampin and exhibited various pulsed-field gel electrophoresis profiles, suggesting the transfer of one of the multiresistance plasmids from the inoculated strains to otherE. colistrains in the intestinal tract. In conclusion, this study clearly illustrates how, inE. coli, “old” antimicrobials may coselect antimicrobial resistance to recent and critical molecules.