Pseudomonas putida group species as reservoirs of mobilizable Tn402-like class 1 integrons carrying blaVIM-2 metallo-β-lactamase genes

Abstract

The Pseudomonas putida group (P. putida G) is composed of at least 21 species associated with a wide range of environments, including the clinical setting. Here, we characterized 13 carbapenem-resistant P. putida G clinical isolates bearing class 1 integrons/transposons (class 1 In/Tn) carrying blaVIM-2 metallo-β-lactamase gene cassettes obtained from hospitals of Argentina. Multilocus sequencing (MLSA) and phylogenetic analyses based on 16S rDNA, gyrB and rpoD sequences distinguished 7 species among them. blaVIM-2 was found in three different cassette arrays: In41 (blaVIM-2-aacA4), In899 (only blaVIM-2), and In528 (dfrB1-aacA4-blaVIM-2). In41 and In899 were associated with complete tniABQC transposition modules and IRi/IRt boundaries characteristic of the Tn5053/Tn402 transposons, which were designated Tn6335 and Tn6336, respectively. The class 1 In/Tn element carrying In528, however, exhibited a defective tni module bearing only the tniC (transposase) gene, associated with a complete IS6100 bounded with two oppositely-oriented IRt end regions. In some P. putida G isolates including P. asiatica, P. juntendi, P. putida G/II, and P. putida G/V, Tn6335/Tn6336 were carried by pLD209-type conjugative plasmids capable of self-mobilization to P. aeruginosa or Escherichia coli. In other isolates of P. asiatica, P. putida G/II, and P. monteiliieilii, however, these blaVIM-2-containing class 1 In/Tn elements were found inserted into the res regions preceding the tnpR (resolvase) gene of particular Tn21 subgroup members of Tn3 transposons. The overall results reinforce the notion of P. putida G members as blaVIM-2 reservoirs, and shed light on the mechanisms of dissemination of carbapenem resistance genes to other pathogenic bacteria in the clinical setting.