Abstract: To study the distribution and molecular characterization of integron-gene cassettes in multidrug-resistant Escherichia coli isolates from food-producing animals in Sichuan province, multiplex PCR was used to detect 3 different classes of integrase genes in 327 isolates. The sequences of the gene cassettes in integron-positive strains were analyzed by PCR-sequencing. The results of multiplex PCR indicated that 294 （89.91%) of 327 isolates harbored intIⅠ, and neither intIⅡ nor intIⅢ was detected in those isolates. 800-3 000 bp amplicons of gene cassettes were yielded in 67 of 81 intIⅠpositive strains choosed randomly. The main cassettes were those encoding aminoglycoside adenyltransferase A (aadA) and dihydrofolate reductase (dfrA, dhfrI). The most prevalent array of gene cassettes was dfrA17+aadA5. aacA4+catB3+dfrA1 and aadA22 were discoveried in two strains, respectively. aadA22 encoding resistance to aminoglycosides was firstly reported in avian E. coli from Sichuan province. IntIⅠwas extensively existed in E. coli isolates. Although there was not a correlation between resistant patterns and integron-gene cassettes in the study, identical gene cassette fragments were found in different strains, suggesting horizontal transfer among different strains may have occurred by integron.

Key words: food-producing animal, Escherichia coli, multidrug-resistance, integron-gene cassettes