Characterization of antibiotic resistance genes linked to class 1 and 2 integrons in strains of Salmonella spp. isolated from swine

The aim of this study was to characterize the antibiotic resistance profiles, the integron-associated resistance determinants, and the potential ability of transferring these determinants by conjugation in Salmonella enterica isolated from swine. Fifty-four strains of Salmonella spp. were isolated from healthy swine. The percentages of resistance, determined by the plate dilution method were as follows: oxytetracycline (41%), streptomycin (39%), sulphamethoxazol+trimethoprim (19%), enrofloxacin-ciprofloxacin (13%), and amoxicillin (0%). The most important resistance serovars were Salmonella Branderburg, Salmonella Derby, Salmonella Typhimurium, and Salmonella Heidelberg. The oxytetracycline-resistant strains amplified the genes tetA (36%), tetB (64%); and the strains resistant to streptomycin and trimethoprim amplified the genes aadA1 (100%) and dfrA1 (100%), respectively. None of the fluoroquinolone-resistant strains amplified the gene qnr. Ten strains amplified the class 1 integron harboring the cassette aadA1. Six strains amplified the class 2 integron harboring the cassettes dfrA1, sat1, and aadA1. The conjugation assays showed that 2 strains transferred the tetA and aadA1 genes and the class 1 integron to a recipient strain. Taken together, the results obtained in this study show a high percentage of resistance in and the presence of integrons in strains of S. enterica isolated from swine. This information should support the implementation of regulations for the prudent use of antimicrobial agents in food-producing animals.