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

The In70.2 integron platform appears to be a conserved structure involved in the dissemination of thebla VIM-1 metallo-β-lactamase gene inPseudomonas aeruginosa . The genetic context of the In70.2 integron platform fromP. 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 theurf2 gene of a Tn3 family transposon of an original structure, named Tn6249 , which also carried a partially deletedmer 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 theendA gene of thePseudomonas 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-producingP. 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 inP. aeruginosa isolates from different geographic locations. The conservation of the genetic context of Tn6249 and Tn6060 suggests anin 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 widespreadP. aeruginosa clonal lineage.