Genomic and molecular characterisation of a KPC-producing Klebsiella pneumoniae clinical isolate resistant to meropenem-vaborbactam, imipenem-relebactam, and ceftazidime-avibactam

Background Resistance to carbapenems and third-generation cephalosporins is increasing in Klebsiella pneumoniae globally, restricting therapeutic options. The β-lactam/β-lactamase inhibitor combinations are widely used to circumvent β-lactamase-mediated resistance. In 2021, an unusual K. pneumoniae clinical isolate, KpMVR1, was recovered from a hospitalised patient in England, exhibiting resistance to meropenem-vaborbactam, imipenem-relebactam, and ceftazidime-avibactam. To investigate this phenomenon, we characterised the genome and antimicrobial susceptibility of KpMVR1 alongside two clonally related isolates susceptible to all three β-lactam/β-lactamase inhibitor combinations: KpMVS1, collected from the same patient 42 days earlier, and KpMVS2, from another patient in the same hospital. Methods Illumina and MinION whole-genome sequencing were conducted for these three isolates, followed by hybrid genome assembly. Annotated genome assemblies were compared to identify genetic variation. Mutagenesis experiments were performed to verify predicted functional alterations. Results All isolates belonged to clone ST8134 and carried bla KPC-2 alleles (KpMVR1: bla KPC-157 ; KpMVS1 and KpMVS2: bla KPC-2 ) in plasmids predicted to be conjugative. Insertion sequence IS Ec68 caused a frameshift mutation in KpMVR1’s ompK36 gene, reducing susceptibility to meropenem-vaborbactam and imipenem-relebactam. KPC-157 demonstrated decreased hydrolysis of imipenem and ceftazidime when compared with KPC-2. KpMVR1 also encoded a disrupted transcriptional repressor MarR and a destabilising mutation in AcrB, a component of the AcrAB-TolC multidrug efflux pump. An intact, iron-transporting fec operon was identified on a novel IncFII(pKP91)/IncFIB(K) plasmid unique to KpMVS2, possibly accounting for the cefiderocol resistance observed in this isolate. Conclusions KpMVR1 carried multiple resistance-associated genetic alterations and likely developed its resistance profile through within-patient evolution. This study highlights the importance of routine screening for resistant pathogens in vulnerable patients to guide antimicrobial chemotherapy and the need to characterise underlying resistance mechanisms to assess the risk of onward dissemination.