Class 1 integron-borne gene cassettes in multidrug-resistant Yersinia enterocolitica strains of different phenotypic and genetic types.

Seventy nine strains of Yersinia enterocolitica resistant to one or more antimicrobials were analyzed for integrons. Only class 1 sul1 integrons containing aadA1a (28 strains), aadA1a-dfr1-sat1 (2 strains), and dfr1-aadA1a (1 strain) gene cassettes were found. The first two types were found in clinical isolates belonging to serotype O:3, biotypes 2 to 4, and eight combined ribotypes, and the third was found in the reference strain, CECT4054 (O:8). All screened resistance markers were found in strains with and without integrons (except for chloramphenicol resistance, encoded by catA1 gene, which was only present in strains with integrons), but in different resistance profiles (R profiles). A profile (ampicillin, streptomycin, sulfadiazine, and trimethoprim resistance, encoded by the tem1, aadA1a, sul1, and dfr1 genes, respectively) was found in strains, with and without integrons. Integrons and some of the resistance genes are located on plasmids with sizes ranging between 65 and 140 kb. This is the first report of class 1 integrons in Y. enterocolitica.