Characterization of Carbapenemase producing Acinetobacter baumannii Isolates from Danish Patients 2014-2021 - Detection of a New International Clone – IC11

The aim of this study was to characterize carbapenemase producing Acinetobacter baumannii isolates from Danish patients using whole genome sequencing (WGS). Furthermore, we compared typing- and epidemiological data for further investigation of the spread and origin of the carbapenemase producing A. baumannii isolates. From January 1st 2014 through September 30th 2021, 141 carbapenemase producing A. baumannii isolates, received at the national reference laboratory at Statens Serum Institut, were investigated using WGS. MLST and cgMLST data, obtained by the SeqSphere+ software, were linked to data related to source of isolation, patient age and gender, hospital admission and travel history. The majority of the carbapenemase producing A. baumannii isolates were from males (n=100, 71%). The majority of patients (n=88, 63%) had travelled outside Scandinavia before admission to a Danish hospital. The most prevalent carbapenemase gene was blaOXA-23 (n=124). Isolates belonging to the dominating international clone IC2 accounted for 79% of all isolates. A new international ST164-OXA-91 clone, proposedly named IC11, was recognized and described. cgMLST analysis revealed 17 clusters, reflecting both sporadic travel to similar geographical areas as well as confirmed outbreaks in Danish hospitals. The occurrence of carbapenemase producing A. baumannii in Denmark was still low; however, isolates belonging to major international clones with a high potential to spread within hospitals, mainly IC2, dominated. OXA-23 was by far the most prevalent carbapenemase detected. Sporadic and travel related introductions to Danish hospitals, but also intra-hospital transmission could be confirmed, emphasizing the need for continuing vigilance.