Comparative Studies of Antimicrobial Resistance in , , and Isolates from Broiler Chickens with and without Use of Enrofloxacin.

This study investigated the effect of enrofloxacin (ENR) administration on the prevalence and antimicrobial resistance of , , and isolated from broiler chickens under field conditions. The isolation rate of was significantly lower ( < 0.05) on farms that administered ENR (6.4%) than on farms that did not (11.6%). The isolation rate was significantly higher ( < 0.05) in farms that administered ENR (6.7%) than in farms that did not (3.3%). The ratio of resistance to ENR was significantly higher ( < 0.05) in isolates from farms that used ENR (88.1%) than farms that did not (78.0%). The respective ratio of resistance to ampicillin (40.5% vs. 17.9%), chloramphenicol (38.0% vs. 12.5%), tetracycline (63.3% vs. 23.2%), and trimethoprim/sulfamethoxazole (48.1% vs. 28.6%) and the ratio of intermediate resistance to ENR (67.1% vs. 48.2%) were significantly higher ( < 0.05) in isolates from the farms that used ENR than farms that did not. In conclusion, the use of ENR at broiler farms was an important factor in decreasing the prevalence of but not and caused ENR resistance among and but not . Exposure to ENR could have a co-selective effect on antimicrobial resistance in enteric bacteria in the field.