Country-wide expansion of a VIM-1 carbapenemase-producing Klebsiella oxytoca ST145 lineage in Poland, 2009–2019

PURPOSE: To elucidate the role of the Klebsiella oxytoca species complex (KoSC) in epidemiology of VIM-type MBL-producing Enterobacterales in Poland. METHODS: The study comprised all 106 VIM-positive KoSC isolates collected by the Polish National Reference Centre for Susceptibility Testing during 2009–2019 from 60 institutions in 35 towns. All isolates were sequenced by Illumina MiSeq, followed by MinION sequencing of selected organisms. Genomes were subjected to bioinformatic analysis, addressing taxonomy, clonality, phylogeny and structural characterisation of key resistance determinants within their chromosomal and plasmidic loci. RESULTS: Among five species identified, K. oxytoca was predominant (n = 92), followed by Klebsiella michiganensis (n = 11). MLST distinguished 18 STs, with the most prevalent Klebsiella oxytoca ST145 (n = 83). The clone segregated a lineage with the In237-like integron [bla(VIM-1)–aacA4 genes; n = 78], recorded in 28 cities almost all over the country. The integron was located in a ~ 49–50 kb chromosomal mosaic region with multiple other resistance genes, linked to a ~ 51 kb phage-like element. The organism might have originated from Greece, and its evolution in Poland included several events of chromosomal ~ 54–258 kb deletions, comprising the natural β-lactamase bla(OXY) gene. A group of other isolates of various species and clones (n = 12) carried the integron In916 on self-transmissible IncA-type plasmids, effectively spreading in Italy, France and Poland. CONCLUSION: KoSC has been one of the major VIM producers in Poland, owing largely to clonal expansion of the specific K. oxytoca–In237-like lineage. Its apparently enhanced epidemic potential may create a danger on international scale. SUPPLEMENTARY INFORMATION: The online version contains supplementary material available at 10.1007/s10096-023-04682-x.