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

Abstract

Many multiresistance plasmids and transposons of gram-negative bacteria carry related DNA elements that appear to have evolved from a common ancestor by site-specific integration of discrete cassettes containing antibiotic resistance genes or sequences of unknown function. The site of integration is flanked by conserved segments coding for an integraselike protein and for sulfonamide resistance, respectively. These segments, together with the antibiotic resistance genes between them, have been termed integrons (H. W. Stokes and R. M. Hall, Mol. Microbiol. 3:1669-1683. We report here the characterization of an integron, InO, from Pseudomonas aeruginosa plasmid pVSI, which has an unoccupied integration site and hence may be an ancestor of more complex integrons. Codon usage of the integrase (int) and sulfonamide resistance (sull) genes carried by this integron suggests a common origin. This contrasts with the codon usage of other antibiotic resistance genes that were presumably integrated later as cassettes during the evolution and spread of these DNA elements. We propose evolutionary schemes for (i) the genesis of the integrons by the site-specific integration of antibiotic resistance genes and (ii) the evolution of the integrons of multiresistance plasmids and transposons, in relation to the evolution of transposons related to Tn2l.

blaCTX-M-2 and blaCTX-M-28 extended-spectrum β-lactamase genes and class 1 integrons in clinical isolates of Klebsiella pneumoniae from Brazil

“…Among Enterobacteriaceae, these resistances were commonly associated with a few types of integrons, mainly class 1 and 2 (Bissonnette & Roy 1992, Partridge & Hall 2003. In this study, two isolates that carried the gene bla CTX-M-2 (K16R and K18P) also contained class 1 integrons with the gene cassettes aadA1 or bla , which encode the enzymes aminoglycoside-3´-adenyltransferase and oxacillinase type 2, respectively.…”

Non‐palindromic attI sites of integrons are capable of site‐specific recombination with one another and with secondary targets

“…1B). The modified plasmid, R388⌬1, contains an integron organized identically to that in the Pseudomonas plasmid, pVS1 (Bissonnette and Roy, 1992) and mediates sulphonamide resistance only.…”

“…The trimethoprim sensitivity of 15 colonies was confirmed by PCR using primers pSph and pHin (Table 5). Two of these colonies, represented by R388⌬1, were checked further by nucleotide sequence determination and were also shown to have lost the ORFA cassette, resulting in a clone carrying only an attI identical to that in pVS1 (Bissonnette and Roy, 1992). All three cassettes were deleted from the integron of R751 to form plasmid 10.005, using a similar strategy to that used to construct R388⌬1.…”

Trimethoprim resistant dihydrofolate reductases in normal faecal flora isolated in India

“…The dhfrV, encoded by Tn2l has not met with the same success, although the Tn2l-like group of transposons is responsible for a wide range of different resistance mechanisms [46]. The integron system associated with the Tn2l-group of transposons has been responsible for the accumulation of resistance mechanisms to sulphonamides [45], ,3-lactams [50], aminoglycosides [51], heavy metals [52] and disinfectants [25] as well as the insertion of the dhfr genes encoding for the DHFR types lIc, V [23], VII [25], X [32].…”

“…Both of these plasmids were isolated from the same village. Many of the transconjugants harbouring the dhfrV were sensitive to sulphamethoxazole (Table 3) which is usually associated with Tn2l and the integrase system of this transposon [46]. Only 3 of those plasmids that did not show hybridization with the tnpA probe were sulphamethoxazole resistant.…”