New cluster of plasmid-located class 1 integrons in Vibrio cholerae O1 and a dfrA15 cassette-containing integron in Vibrio parahaemolyticus isolated in Angola

Abstract

The resistance profile and its correlation with mobile genetic elements were investigated in 11 Vibrio cholerae O1 and 2 Vibrio parahaemolyticus clinical isolates, as well as in 1 V. cholerae O1 and 1 V. cholerae non-O1 environmental isolate, isolated between 1991 and 1996 in different provinces of Angola. All clinical isolates of V. cholerae O1 were resistant to ampicillin, chloramphenicol, trimethoprim, sulfamethoxazole, and tetracycline. They also contained a large conjugative plasmid (p3iANG) with a set of three class 1 integrons harboring dfrA15, blaP1, and qacH-aadA8 cassettes, which code for resistance to trimethoprim, beta-lactams, quaternary ammonium compounds, and aminoglycosides, clustered in a 19-kb region. Chloramphenicol (cat1), kanamycin (aph), sulfonamide (sul2), and tetracycline (tetG) resistance genes were also carried on the plasmid within the same 19-kb region. A chromosomal integron containing the dfrA15 cassette was also revealed in V. parahaemolyticus strains. SXT integrase genes were present in six V. cholerae isolates but apparently were not associated with known SXT-associated resistance genes. This study indicates that plasmids and integrons contributed mainly to the circulation of multiple-drug resistance determinants in Vibrio strains from Angola.

FIG. 1.

Map of the 19-kb region on the p3iANG plasmid, clustering together the three integrons and chloramphenicol, kanamycin, and tetracycline resistance genes (approximate sizes; not to scale). The upper and lower lines represent the amplicons obtained by the primer pairs as indicated and oriented by arrows. Primer pairs and resulting amplicons for sequencing the 3.30-kb amplicon are described in the text; the 140-bp junction between the two integrons is indicated by the solid black rectangle. Sequence DQ227350 corresponds to the 3.3-kb 3′CSrev/5′CSrev amplicon. Sequence DQ149925 corresponds to the contiguous 1.5-kb In-F/In-B amplicon.