Molecular epidemiology of extended-spectrum beta-lactamase-producing Klebsiella pneumoniae bloodstream infections from Aberdeen, Scotland, and their comparison to isolates from England

<i>Klebsiella</i> spp., the second leading cause of bacteraemia in the UK, are major nosocomial pathogens. We investigated the epidemiology of extended-spectrum <i>β</i>-lactamase (ESBL)-producing <i>Klebsiella</i> spp. in Aberdeen, Scotland and England. Twenty-four ESBL producers underwent whole-genome sequencing and typing using MLST. Sequence types were queried in the Bacterial Isolate Genome Sequence Database (BIGSdb) to assess phylogenetic relationships using Parsnp, and resistance/virulence genes were identified by Kleborate. Plasmids were assembled with plasmidSPAdes. All isolates had the <i>bla</i> _SHV, with three positive for <i>bla</i> _SHV-12 ESBL and two positive for <i>bla</i> _DHA-1 ESBL. The <i>bla</i> _CTX-M was observed in 71% (33% plasmid-borne), <i>bla</i> _TEM in 42%, with all isolates resistant to ceftazidime, cefotaxime and cefuroxime. Two isolates carried <i>mcr-9.1</i> on 2.5 and 203 kb plasmids. MLST identified 21 strains, with ST-13 and ST-200 being the most common. BIGSdb revealed 487 similar strains across 43 clonal groups. ST14 (34%) and ST15 (29%) were predominant multidrug-resistant strains. Nearly all isolates (99%) harboured the <i>bla</i> _SHV (43% SHV-28, 2% SHV-12 ESBL), and 57% carried a <i>bla</i> _CTX-M. Carbapenemases were detected in 61% of isolates, and 59% had <i>gyr</i>A/<i>par</i>C mutations, exclusively linked to strains from England. ST432 strains from humans (resistant) and cattle (sensitive) were closely related. We also observed ST14 and ST15 (CC15) as high-risk clones thought to have evolved independently that are globally prevalent. The coexistence of <i>mcr-9.1</i> and plasmid ESBL <i>bla</i> _CTX-M in <i>Klebsiella</i> spp. threatens the efficacy of critically important antibiotics. The close relatedness of human and cattle ST432 strains suggests potential zoonotic transmission, emphasizing the role of livestock as a reservoir for antimicrobial-resistant pathogens and the need for genomic epidemiology studies to elucidate transmission pathways and interspecies exchange. A One Health approach integrating human, animal and environmental surveillance would enhance our understanding of the molecular dynamics and evolutionary trajectory of <i>Klebsiella pneumoniae</i>, reinforcing the need for targeted interventions to limit the spread of antimicrobial resistance.