Double carbapenemases in blood isolates: dissemination in a single medical center via multiple plasmids and a variety of highly efficient clones.

Acquisition of multiple carbapenemase genes by (Kp) is an emerging public health threat. Here, we aim to elucidate the population structure of Kp blood isolates carrying two different carbapenemase genes and identify the mechanism facilitating their dissemination. The study was conducted in a tertiary healthcare center between 2014 and 2022. Twenty-four patients with bacteremia caused by Kp carrying two different carbapenemase genes were identified. All 24 blood isolates were analyzed by short-read genome sequences supplemented by long reads in a selected number of isolates. All isolates carried (23 , 1 ) and genes, along with a variety of antimicrobial resistance determinants. The isolates were clustered in six clonal lineages (ST39, ST147, ST323, ST258, ST3035, and ST340). Long-read genome sequences demonstrated that each carbapenemase gene was located in a separate group of plasmids: the on a fusion of IncFIB(pQil) and IncFII(K) plasmids, the on IncX3, the on IncC, or a fusion of the IncFIB(pNDM-Mar) and IncHI1B(pNDM-MAR) plasmids. Comparison of plasmid content of eight isolates carrying a single carbapenemase gene from a previous study with eight isolates carrying two carbapenemase genes from the present study, matched by clonal lineages, revealed that the second carbapenemase gene was acquired by addition of another plasmid. Identical plasmids were found within the same lineage and across lineages. These findings suggest that dissemination of carbapenemase genes in our hospital setting was driven by multiple plasmids across a variety of highly efficient clones.