Department of Microbiology, Royal North Shore Hospital, Australia.
Southern hybridization analysis of the IncC plasmid pDGO100 showed that, in addition to the well-characterized integron In7, there is a second integron which is located on a 3.6-kb BamHI fragment. This integron also possesses the qacE delta l and sulI genes typically found as part of the 3'-conserved segment of integrons. The 3.6-kb BamHI fragment, when cloned into pUC19 to form pDGO301, conferred resistance to trimethoprim as well as sulfamethoxazole. The DNA sequence of the trimethoprim resistance gene in pDGO301 was determined and it was shown that the gene was precisely inserted as a cassette in an integron with 100% identity to the trimethoprim resistance gene dfrA7.