Composite integron array generated by insertion of an ORF341-type integron within a Tn21-like element.
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.
Villa
Laura
L
Laboratory of Bacteriology and Medical Mycology, Istituto Superiore di Sanità, Rome, Italy.
Visca
Paolo
P
Tosini
Fabio
F
Pezzella
Cristina
C
Carattoli
Alessandra
A
D000595:Amino Acid Sequence; D001483:Base Sequence; D003001:Cloning, Molecular; D003062:Codon / Q000235:genetics; D017931:DNA Primers; D004351:Drug Resistance / Q000235:genetics; D015964:Gene Expression Regulation, Bacterial / Q000235:genetics*; D005798:Genes, Bacterial / Q000235:genetics*; D008969:Molecular Sequence Data; D010957:Plasmids / Q000235:genetics; D020133:Reverse Transcriptase Polymerase Chain Reaction; D019779:Salmonella enterica / Q000235:genetics*; D014296:Trimethoprim Resistance / Q000235:genetics
D003062:Codon; D017931:DNA Primers