Phenotypic and molecular characterizations of carbapenem-resistant Acinetobacter baumannii isolates collected within the EURECA study.

Multi-drug-resistant Acinetobacter baumannii isolates are key pathogens that contribute to the global burden of antimicrobial resistance. This study aimed to investigate the phenotypic and molecular characteristics of carbapenem-resistant A. baumannii (CRAB) isolates from the EURECA clinical trial. In total, 228 CRAB clinical strains were recovered from 29 sites in 10 European countries participating in the EURECA study between May 2016 and November 2018. All strains were reconfirmed centrally for identification and antimicrobial susceptibility testing, and were then subjected to DNA isolation and whole-genome sequencing (WGS), with analysis performed using BacPipe v.1.2.6. K and O typing was performed using KAPTIVE. Overall, 226 (99.1%) strains were confirmed as CRAB isolates. The minimum inhibitory concentration (MIC90) results of imipenem and meropenem were >16 mg/L. WGS showed that the isolates mainly harboured blaOXA-23 (n=153, 67.7%) or blaOXA-72 (n=70, 30.1%). Four blaOXA-72 isolates from Serbia co-harboured blaNDM-1. An IS5 transposase family element, ISAba31, was found upstream of the blaOXA-72 gene harboured on a small (~10-kb) pSE41030-EUR plasmid. The majority of isolates (n=178, 79.1%) belonged to international clone II. Strains belonging to the same sequence type but isolated in different countries or within the same country could be delineated in different clusters by core-genome multi-locus sequence typing (MLST). Whole-genome/core-genome MLST showed high diversity among the isolates, and the most common sequence type was ST2 (n=153, 67.7%). The EURECA A. baumannii strain collection represents a unique, diverse repository of carbapenem-resistant isolates that adds to the existing knowledge of A. baumannii epidemiology and resistance genes harboured by these strains.