Molecular epidemiology of metallo-beta-lactamase-producing Pseudomonas aeruginosa isolates from Norway and Sweden shows import of international clones and local clonal expansion

Abstract

Scandinavia is considered a region with a low prevalence of antimicrobial resistance. However, the number of multidrug-resistant (MDR) Gram-negative bacteria is increasing, including metallo-beta-lactamase (MBL)-producing Pseudomonas aeruginosa. In this study MBL-producing P. aeruginosa isolates identified in Norway (n = 4) and Sweden (n = 9) from 1999 to 2007 were characterized. Two international clonal complexes (CC), CC111 (n = 8) and CC235 (n = 2), previously associated with MBL-producing isolates, were dominant. CC111 isolates (ST111/229; serotype O12; bla(VIM-2)) included clonally related isolates identified in Skåne County, Sweden (n = 6), and two isolates associated with importation from Greece and Denmark. In all CC111 isolates, bla(VIM-2) was located in integron In59.2 or In59 variants. The two CC235 isolates (ST235/ST230; serotype O11; bla(VIM-4)) were imported from Greece and Cyprus, were possibly clonally related, and carried bla(VIM-4) in two different integron structures. Three isolates imported from Ghana (ST233; serotype O6; bla(VIM-2)), Tunisia (ST654; serotype O11; bla(VIM-2)), and Thailand (ST260; serotype O6; bla(IMP-14)) were clonally unrelated. ST233 was part of a new CC (CC233) that included other MBL-producing isolates, while ST654 could also be part of a new CC associated with MBL producers. In the isolates imported from Ghana and Tunisia, bla(VIM-2) was part of unusual integron structures lacking the 3' conserved segment and associated with transposons. The bla(VIM) gene was found to be located on the chromosome in all isolates. Known risk factors for acquisition of MBL were reported for all patients except one. The findings suggest that both import of successful international clones and local clonal expansion contribute to the emergence of MBL-producing P. aeruginosa in Scandinavia.

FIG. 1.

Schematic view (not to scale) of the genetic context surrounding the MBL genes in Norwegian and Swedish MBL-producing P. aeruginosa isolates. (A) Isolates U9-19005, AK-5493, B4-25753, BU-20287, BU-43038, BU-36178, and BNL-1681 (GenBank accession numbers FN397626, FN397624, FN397621, FN397619, FN397622, FN397620, and FN397625). (B) Isolate K45-32 (GenBank accession number FN397618). (C) Isolate K34-7 (GenBank accession number FM165436). (D) Isolate PA66 (GenBank accession number AY866525). (E) Isolate K34-73 (GenBank accession number FN397623). (F) Isolate OS-210 (GenBank accession number FN397628). (G) Isolate K44-24 (GenBank accession number FN397627). The genetic structures of isolate PA66, AK-5493, and K34-7 were determined previously (12, 32). Open reading frames are represented by arrows indicating the orientation. MBL genes are shown in grey. The 59-be of each gene cassette is represented by an open circle and the attI site by a gray oval. The partial 5′ CS in front of the sul1 gene of OS-210 (F) is represented by an open rectangle. The inverted repeat of Tn5501 is indicated by a black rectangle, and the inverted repeat of Tn5393 is indicated by a gray rectangle.