Maurizio Sanguinetti

Bloodstream infection (BSI) caused by carbapenem-resistant Klebsiella pneumoniae (KP) poses significant challenges, particularly when the infecting isolate carries multiple antimicrobial resistance (AMR) genes/determinants. This study, employing short- and long-read whole-genome sequencing, characterizes six New Delhi metallo-β-lactamase (NDM) 1 and KP carbapenemase (KPC) 3 co-producing KP isolates, the largest cohort investigated in Europe to date. Five [sequence type (ST) 512] and one (ST11) isolates were recovered from patients who developed BSI from February to August 2022 or February 2023 at two different hospitals in Rome, Italy. Phylogenetic analysis revealed two distinct clusters among ST512 isolates and a separate cluster for the ST11 isolate. Beyond bla NDM-1 and bla KPC-3 , various AMR genes, indicative of a multidrug resistance phenotype, including colistin resistance, were found. Each cluster-representative ST512 isolate harbored a bla NDM-1 plasmid (IncC) and a bla KPC-3 plasmid [IncFIB(pQil)/IncFII(K)], while the ST11 isolate harbored a bla NDM-1 plasmid [IncFII(pKPX1)] and a bla KPC-3 plasmid [IncFIB(K)/IncFII(K)]. The bla NDM-1 plasmids carried genes conferring resistance to clinically relevant antimicrobial agents, and the aminoglycoside resistance gene aac ( 6 ′)- Ib was found on different plasmids. Colistin resistance-associated mgrB / pmrB gene mutations were present in all isolates, and the yersiniabactin-encoding ybt gene was unique to the ST11 isolate. In conclusion, our findings provide insights into the genomic context of bla NDM-1 / bla KPC-3 carbapenemase-producing KP isolates. IMPORTANCE This study underscores the critical role of genomic surveillance as a proactive measure to restrict the spread of carbapenemase-producing KP isolates, especially when key antimicrobial resistance genes, such as bla NDM-1 / bla KPC-3 , are plasmid borne. In-depth characterization of these isolates may help identify plasmid similarities contributing to their intra-hospital/inter-hospital adaptation and transmission. Despite the lack of data on patient movements, it is possible that carbapenem-resistant isolates were selected to co-produce KP carbapenemase and New Delhi metallo-β-lactamase via plasmid acquisition. Studies employing long-read whole-genome sequencing should be encouraged to address the emergence of KP clones