Composite integron array generated by insertion of an ORF341-type integron within a Tn21-like element

Microb Drug Resist. Spring 2002;8(1):1-8. doi: 10.1089/10766290252913692.


Two class 1 integrons, In-t1 and In-t2, were previously identified in IncFI plasmids of Salmonella enterica serotype Typhimurium. Molecular analysis revealed a close physical link between the two integrons. In-t1 is preceded by the transposase genes of Tn21, whereas In-t2 is located downstream the 3'-conserved segment (3'-CS) of In-t1, in a head-to-tail configuration. In-t1 shows a peculiar sequence downstream the 3'-CS, containing an extended version of the open reading frame known as ORF341 (referred to as ORF341E) and a novel trimethoprim resistance gene, designated dfrA18. Retrospective analysis provided evidence for In-t1 insertion within Tn1935, a Tn21-related transposon identified in IncFI plasmids circulating among epidemic clones of multidrug-resistant S. enterica during the 1970s. Structural comparison between Tn21 derivatives from recent and ancestor IncFI plasmids showed that In-t2 has been conserved by these replicons. In-t1 belongs to a novel family of class 1 integrons containing the ORF341E sequence, and appears to have been acquired by IncFI plasmids after the assembly of Tn1935. In-t1 insertion occurred within the 5'-conserved segment (5'-CS) proximal region of the resident In-t2.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Amino Acid Sequence
  • Base Sequence
  • Cloning, Molecular
  • Codon / genetics
  • DNA Primers
  • Drug Resistance / genetics
  • Gene Expression Regulation, Bacterial / genetics*
  • Genes, Bacterial / genetics*
  • Molecular Sequence Data
  • Plasmids / genetics
  • Reverse Transcriptase Polymerase Chain Reaction
  • Salmonella enterica / genetics*
  • Trimethoprim Resistance / genetics


  • Codon
  • DNA Primers

Associated data

  • GENBANK/AF028594
  • GENBANK/AF231986