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.

resistance against antimicrobials that are critical for human and veterinary medicine, representing a major threat for public health. Additionally, these strains could have a competitive advantage in the presence of antimicrobial selective pressure, leading to an increase in food contamination. This study highlights the need for coordinated local and global actions regarding the use of antimicrobials in animal food production.

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Salmonella spp. isolates obtained from healthy swine in 2008 were analyzed for antibiotic resistance phenotypes and genotypes. The resistance profiles of the 2008 isolates were compared with those of a Salmonella collection isolated from the same geographical area in 2005. The 2008 isolates consisted of strains that were 97% oxytetracycline resistant, 33.3% amoxicillin resistant, 31.8% amoxicillin- plus clavulanic acid resistant, 27.5% trimethoprim-sulfamethoxazole resistant, 17.3% streptomycin resistant, and 7.2% enrofloxacin-ciprofloxacin resistant. The presence of integrons and resistance genes and their topological association in resistant strains was assessed by PCR. The prevalence of class 1 integrons was the highest, at 46.2%, while class 2 integrons were present in 17.9% of the isolates. In strains that harboured class 1 integrons, we identified 3 different gene cassette arrangements; a single class 2 integron arrangement of dfrA1-sat1-aadA1 was found. Comparison of these results with data obtained from the 2005 isolates showed that Salmonella strains resistant to amoxicillin and amoxicillin plus clavulanic acid had clearly emerged over the span of 3 years, along with an increase in the prevalence of class 1 integrons and the acquisition of new gene cassette arrangements. These findings highlight the need for continual monitoring of regional isolates to establish more efficient vigilance programs that can address variations in resistance over short periods of time within the same geographical area.