Occurrence and Characteristics of Class 1 and Class 2 Integrons in Resistant Escherichia coli Isolates from Animals and Farm Workers in Northeastern China

The purpose of this study was to investigate the incidence of class 1 and class 2 integrons and the presence of gene cassettes in resistant Escherichia coli isolates from farm animals and farm workers in northeastern China during 2004-2007. Most of the E. coli isolates from the farm workers and animals were mutiresistant and showed high resistance to aminoglycosides, chloramphenicol, amoxicillin, sulfanilamide, and quinolones. Integrons were found in 56.8% of the resistant E. coli isolates from the animals and farm workers. Integrase genes were detected in 58.7% (101/172), 60.4% (64/106), and 26.1% (6/23) of resistant E. coli isolates from the swine, chickens, and farm workers, respectively. Class 2 integrons were detected only in resistant E. coli isolates from the chickens and have one array cassette of dfrA1-sat1-aadA1-orfX. Dfr17-aadA5 was the most prevalent in resistant E. coli isolates from the farm workers, swine, and chickens. Conjugative experiments demonstrated horizontal transfer of class 1 and class 2 integrons between isolates of farm worker and animals. Our data revealed that multidrug resistance and class 1 integrons were widely present in E. coli isolates obtained in northeastern China. The horizontal transfer of integrons by conjugation seems to contribute to the wide dissemination of antimicrobial resistance in E. coli isolates of human and animal origin.