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Objectives: NDM-producing Enterobacteriaceae clinical isolates remain uncommon in the European region. We describe the emergence and broad dissemination of one successful NDM-1-producing Klebsiella pneumoniae clone in Greek hospitals.Methods: During a 4 year survey (January 2013-December 2016), 480 single-patient carbapenem non-susceptible K. pneumoniae isolates, phenotypically MBL positive, were consecutively recovered in eight Greek hospitals from different locations and subjected to further investigation. Antimicrobial susceptibility testing, combined-disc test, identification of resistance genes by PCR and sequencing, molecular fingerprinting by PFGE, plasmid profiling, replicon typing, conjugation experiments and MLST were performed.Results: Molecular analysis confirmed the presence of the blaNDM-1 gene in 341 (71%) K. pneumoniae isolates. A substantially increasing trend of NDM-1-producing K. pneumoniae was noticed during the survey (R2 = 0.9724). Most blaNDM-1-carrying isolates contained blaCTX-M-15, blaOXA-1, blaOXA-2 and blaTEM-1 genes. PFGE analysis clustered NDM-1 producers into five distinct clonal types, with five distinct STs related to each PFGE clone. The predominant ST11 PFGE clonal type was detected in all eight participating hospitals, despite adherence to the national infection control programme; it was identical to that observed in the original NDM-1 outbreak in Greece in 2011, as well as in a less-extensive NDM-1 outbreak in Bulgaria in 2015. The remaining four ST clonal types (ST15, ST70, ST258 and ST1883) were sporadically detected. blaNDM-1 was located in IncFII-type plasmids in all five clonal types.Conclusions: This study gives evidence of possibly the largest NDM-1-producing K. pneumoniae outbreak in Europe; it may also reinforce the hypothesis of an NDM-1 clone circulating in the Balkans. [ABSTRACT FROM AUTHOR]