Phenotypic and Genotypic Characterization of Antibiotic Resistance Integrons in Salmonella enterica serovar Newport

Soto, Raymond
Numerous recent outbreaks of Salmonella enterica have been found to be resistant to multiple antibiotics, which only exacerbates an already serious infection. Integrons, which are mobile DNA elements, have been found in previous studies to contribute to antibiotic resistance. Two consistently observed integrons (1.0 kb and 1.2 kb) were cloned and introduced into an antibiotic sensitive strain of Escherichia coli. Upon phenotypic characterization, the 1.0 kb integron was found to confer resistance to streptomycin. Genotypic characterization supported this finding with the presence of an adenylyl transferase (aadA) gene in the integron cassette. The 1.2 kb integron was cloned and characterized, phentoytpically it was shown that resistance to trimethoprim was conferred, this was supported genotypically by the identification of a dihydrofolate reductase (dfrA) gene located in the integron. The 1.8 kb integron was not successfully cloned. Attempts to move the 1.2 kb integron between Salmonella species failed, however, the movement of a mercury resistance plasmid was observed indicating a potential for genetic transfer between species. This characterization demonstrated that these integrons contribute to the antibiotic resistance profile observed in the Salmonella enterica.
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