High Rate of Multidrug Resistance and Integrons in Escherichia coliisolates from Diseased Ducks in Select Regions of China

With the increasing number of ducks being raised and consumed, it is crucial to monitor the presence of multi-drug resistant (MDR)bacteria in duck farming. Waterfowl, such as ducks, can contribute to the rapid dissemination of antibiotic resistance genes (ARGs). The objective of this study was to investigate the antimicrobial resistance (AMR), ARGs, and mobile genetic elements (MGEs), such as IS26, tbrC, ISEcp1in Escherichia coli(E. coli)isolated from the intestinal contents of diseased ducks between 2021 and 2022 in Sichuan, Chongqing and Anhui, China. The AMR phenotypes of 201 isolated E. colistrains were determined using the minimum inhibitory concentrations (MICs)method. Subsequently, polymerase chain reaction (PCR)and sequencing techniques were employed to screen for integron-integrase genes (intI1, intI2, intI3genes), gene cassettes (GCs), MGEs, and ARGs. The results demonstrated that 96.5% of the isolates were resistant to at least one antibiotic, with 88.1% of the strains displaying MDR phenotype. The highest AMR phenotype observed was for trimethoprim-sulfamethoxazole (88.1%). Furthermore, class 1 and class 2 integrons were detected in 68.2% and 3.0% of all the isolates, respectively, while no class 3 integrons were found. Ten types of GCs were identified in the variable regions of class 1 and class 2 integrons. Moreover, 10 MGEs were observed in 46 combinations, with IS26exhibiting the highest detection rate (89.6%). Among the 22 types of ARGs, tetA (77.1%) was the most frequently detected. In the conjugational transfer experiment, transconjugants were found to carry specific ARGs and MGEs, with their MIC values were significantly higher than those of recipient E. coliJ53, indicating their status as MDR bacteria. This study emphasizes the necessity of monitoring MGEs, ARGs, and integrons in duck farms. It provides valuable insights into the complex formation mechanisms of AMR and may aid in preventing and controlling the spread of MDR bacteria in waterfowl breeding farm.