Evolutionary relationship between Tn21-like elements and pBP201, a plasmid from Klebsiella pneumoniae mediating resistance to gentamicin and eight other drugs

Abstract

We have characterized pBP201 one of the plasmids from a collection of 46 strains producing adenylyltransferase ANT(2") (Schmidt 1984). It confers resistance to sulphonamides and produces aminoglycoside adenylyltransferases AAD(3") and ANT(2") and beta-lactamase TEM-1. Plasmid pBP201 has a size of 24.8 kilobases (kb) and contains TnA and a Tn21-related element, Tn4000 delta, with deletions in mer and the termini and a substitution at tnpR. In complementation assays with transposition-deficient mutants of Tn21 the element in pBP201 appears to be TnpA+ but TnpR-. It represents a naturally occurring defective transposon. The sequence organization of pBP201 has been compared with that of Tn21-related elements such as Tn2410, Tn2603, Tn2424, Tn1696, and Tn4000. In these transposons the integration sites of resistance genes cat, bla, aacA, aacC or aadB have been identified at two preferential locations; these are at the termini of the streptomycin resistance gene aadA. Two additional sites have been localized in the Tn21 backbone to the right of the mer operon and at res (internal resolution site) and are probably involved in the evolution of these elements. Based on these results a model for the possible genealogy of class II transposons is presented.

Characterization of In0 of Pseudomonas aeruginosa plasmid pVS1, an ancestor of integrons of multiresistance plasmids and transposons of gram-negative bacteria

“…Also, the 59-base element supplied by the first cassette may favor subsequent integrations on either side of the aadA cassette, as shown for the aadA stems in Fig. 3 (42,55,60 (Fig. 4) …”

“…The evolution of some of these elements, specifically the Tn21-like transposons and related plasmids, by site-specific integration of antibiotic resistance genes has been described in recent years (3,11,32,42,60,61). These elements have been shown to possess a common structure, the integron (Fig.…”

“…This 3'-conserved segment would contain another crossover point (3) where the integration of DNA elements of various sizes (loops 1, 2, and 3 [see below]) can occur. According to restriction maps and heteroduplex analysis, some plasmids such as R388 seem to lack the distal 2.7-kb region of the 3'-conserved segment adjacent to sull and ORF5 (29,39,42,58). This segment could have been deleted or additional segments could have been integrated at crossover point 3 by recombinational events of unknown nature.…”

Evolutionary perspectives on multiresistance beta-lactamase transposons

“…1-Lactamase genes are part of transposons, and it remains to be established how they became associated with these elements (19,31). Single-resistance determinants have been shown to be part of transposons, such as in Tn3.…”

Characterization of the nonenzymatic chloramphenicol resistance (cmlA) gene of the In4 integron of Tn1696: similarity of the product to transmembrane transport proteins

“…The characterization of multiresistance elements, plasmids and transposons, related to bacterial transposon Tn2J revealed that rearrangements involving antibiotic resistance genes were occurring in the vicinity of the streptomycin-spectinomycin (aadA) and sulfonamide (sull) resistance regions (20,40,50,56,62,63). Stokes and Hall (55) have defined the elements borne on these multiresistance plasmids and transposons as integrons, a novel family of potentially mobile DNA elements which are composed of two conserved segments between which discrete units, ordinarily antibiotic resistance genes, have been integrated as gene cassettes.…”