Genetic characterization of antibiotic resistance genes linked to class 1 and class 2 integrons in commensal strains of Escherichia coli isolated from poultry and swine.

The aim of this research was to identify the presence of integrons among Escherichia coli strains isolated from poultry and swine and to characterize the topological association of these integrons with resistance genes and assess their potential ability to transfer these elements by conjugation. One hundred and seventy-two strains of E. coli were isolated. Their resistance to tetracycline, streptomycin, sulfamethoxazole-trimethoprim, ciprofloxacin, and enrofloxacin was studied by plate dilution. In resistant strains the presence of integrons and resistance genes was assessed by PCR. In the variable region, genes aadA1, dfrA1, and qnr were analyzed. Also, presence of tetA, tetB, and sul1 was assessed. Transference of these genes and integrons in vitro was evaluated by conjugation assays, using E. coli J53 Az(r) as recipient strain. Seventy-eight percent and 83% of the poultry and swine strains, respectively, were resistant to at least one of the studied antimicrobials. Of the isolated strains 91 presented integrons. Resistance genes detected within the integrons were aadA1, dfrA1, and sat1. Gene qnr was not detected. Genes tet and sul1 were identified in 105 and 53 strains, respectively. Seven strains transferred their resistance determinants by conjugation. The results verify the high percentage of antibiotic resistance in the E. coli strains isolated, and these represent a reservoir of resistance genes and integrons.