High prevalence of clonally related ST182 NDM-1-producing Enterobacter cloacae complex clinical isolates in Greece.

NDM-type metallo-β-lactamase (MBL)-producing Enterobacterales remain uncommon in the European region, especially among species other than Klebsiella pneumoniae and Escherichia coli. The aim of this study was to describe epidemiological and molecular characteristics of a widespread NDM-1-producing Enterobacter cloacae complex outbreak in Greece. Over a 6-year period (March 2016-March 2022), a retrospective study was conducted in a tertiary care Greek hospital. Ninety single-patient carbapenem-non-susceptible E. cloacae complex clinical isolates were recovered consecutively. The isolates were subjected to further investigation, including antimicrobial susceptibility testing and combined disc tests for carbapenemase production, polymerase chain reaction and sequencing for resistance genes, molecular fingerprinting by pulsed-field gel electrophoresis (PFGE), plasmid profiling, replicon typing, conjugation experiments, genotyping by multi-locus sequence typing (MLST), whole-genome sequencing and phylogenetic analysis. Phenotypic and molecular testing confirmed the presence of bla in 47 (52.2%) of the E. cloacae complex isolates. MLST analysis clustered all but four of the NDM-1 producers into a single MLST sequence type (ST182), whereas single isolates belonged to different sequence types (ST190, ST269, ST443 and ST743). PFGE analysis revealed that ST182 isolates were clustered into a single clonal type, with three subtypes, which differed from the clonal types detected among the remaining carbapenem non-susceptible E. cloacae complex isolates identified during the study period. All ST182 bla-carrying isolates also harboured the bla AmpC gene, while the bla, bla and bla genes were detected in most cases. In all clonal isolates, the bla gene was located on an IncA/C-type plasmid, and flanked upstream by an ISAba125 element and downstream by ble. Conjugation experiments failed to produce carbapenem-resistant transconjugants, indicating a low dynamic for horizontal gene transfer. Application of enforced infection control measures led to the absence of new NDM-positive cases for periods of time during the survey. This study represents the largest clonal outbreak of NDM-producing E. cloacae complex in Europe.