Tn 6249 , a New Tn 6162 Transposon Derivative Carrying a Double-Integron Platform and Involved with Acquisition of the bla _VIM-1 Metallo-β-Lactamase Gene in Pseudomonas aeruginosa

Abstract

cThe In70.2 integron platform appears to be a conserved structure involved in the dissemination of the bla VIM-1 metallo-␤-lactamase gene in Pseudomonas aeruginosa. The genetic context of the In70.2 integron platform from P. aeruginosa VR-143/97, the VIM-1-producing index strain isolated in Italy in 1997, was fully characterized by a next-generation sequencing approach refined by conventional sequencing. The In70.2 integron platform from VR-143/97 was found to be associated with a defective Tn402-like transposon inserted into the urf2 gene of a Tn3 family transposon of an original structure, named Tn6249, which also carried a partially deleted mer operon and an In90 integron platform in a tail-to-tail orientation. Tn6249 was inserted into a PACS171b-like genomic island, which was in turn inserted into the endA gene of the Pseudomonas chromosomal backbone. Tn6249 showed a similar structure and a conserved location with respect to that of Tn6060, a Tn3 family transposon associated with In70.2 and carrying a double-integron platform, which was detected in a VIM-1-producing P. aeruginosa strain isolated in Australia in 2008. Both Tn6249 and Tn6060 are apparently derived from Tn6162, a mercury resistance transposon carrying an integron platform, which was found in P. aeruginosa isolates from different geographic locations. The conservation of the genetic context of Tn6249 and Tn6060 suggests an in situ evolution of these elements after the insertion of a Tn6162-like ancestor into the PACS171b-like genomic island (GI) present in the genome of a successful widespread P. aeruginosa clonal lineage. Metallo-␤-lactamases (MBLs) have emerged as a major threat to antimicrobial chemotherapy due to their extended-spectrum activity against most ␤-lactams, including carbapenems, and their resistance to ␤-lactamase inhibitors, such as clavulanate, sulbactam, tazobactam, and avibactam (1). Among the several acquired MBLs reported in Gram-negative pathogens, the VIM-type enzymes have been detected worldwide in a large number of species, including Pseudomonas aeruginosa, other Gram-negative nonfermenters (GNNFs), and Enterobacteriaceae, and together with the IMP and NDM types, they are currently the MBLs with the greatest epidemiological and clinical impact (1-3). In P. aeruginosa, VIM-type enzymes are overall the most widespread and prevalent acquired MBLs (1, 4-7).Genes encoding VIM-type MBLs are usually carried on mobile gene cassettes associated with class 1 integron platforms (8), and integron-mediated cassette mobility has contributed to their dissemination, as indicated by the finding of bla VIM gene cassettes as part of different cassette arrays (9, 10). On the other hand, class 1 integron platforms are associated with functional or defective Tn402-like transposons, which preferentially target the res sites of plasmids and transposons of the Tn3 family (11-13), thus establishing genetic linkages that may further contribute to the mobility of the integron platforms (8).In P. aeruginosa VR-143/97, the bla VIM-1 index strain is...

Genomic islands 1 and 2 play key roles in the evolution of extensively drug-resistant ST235 isolates of Pseudomonas aeruginosa

“…In conclusion, all three Sydney ST235 isolates have the bla GES-5 gene inserted as a gene cassette within a class 1 integron that forms part of Tn 6163 located in GI2 . The genomic data presented here and elsewhere (AP014622, AP014646 and [ 29 ]) show that genomic islands are playing a seminal role in the dissemination of resistance to a wide range of clinically important antibiotics, including metallo-β-lactams and extended-spectrum β-lactams. It is not known if GI1 and GI2 can be mobilized to other Gram-negative bacteria.…”

“…In P. aeruginosa strain VR-143/97, the bla VIM-1 metallo-β-lactamase gene cassette is associated with a class 1 integron (In70.2) in a defective Tn 402 -like transposon that is inserted in the urf2 gene of a Tn 3- derivate transposon known as Tn 6249 . Like Tn 6060 , Tn 6249 has a complex structure and carries two class 1 integrons (In90 and In70.2) in a tail-to-tail orientation [ 29 ]. Tn 6249 is located in a PACS171b-like genomic island, described earlier as GI1 in relation to Tn 6060 [ 25 ] , within the endA gene of the P. aeruginosa chromosome [ 29 ].…”

“…Like Tn 6060 , Tn 6249 has a complex structure and carries two class 1 integrons (In90 and In70.2) in a tail-to-tail orientation [ 29 ]. Tn 6249 is located in a PACS171b-like genomic island, described earlier as GI1 in relation to Tn 6060 [ 25 ] , within the endA gene of the P. aeruginosa chromosome [ 29 ]. Tn 6249 shares structural identity with Tn 6060, although the gene cassettes carried by In90 are different and a part of the Tn 3 backbone is missing in Tn 6249 [ 25 ].…”

“…Notably, Tn 6162 is also located at an identical position in the genomic backbone of GI1 as Tn 6060, but has a simpler complex resistance locus (CRL) consisting of one class 1 integron. Consequently, it has been hypothesized that insertion of a Tn 6162 -like ancestor into the PACS171b-like genomic island (VR-143/97; 51 424 nt) preceded the genetic events that gave rise to Tn 6249 and Tn 6060 in clonally dispersed lineages of P. aeruginosa [ 29 ].…”

Mobile Genetic Elements Associated with Antimicrobial Resistance

“…It is not clear whether a GI designated GI1 (different from PAGI-1), inserted into the endA gene, would also be classified as an ICE. Variants with different class 1 In/Tn structures associated with Tn1403, or remnants of it, carry bla VIM-1 and other cassettes (425,428,(432)(433)(434).…”