Genomic, virulent and phenotypic characterization of a cerebrospinal fluid-derived ST86-KL2 hypervirulent Klebsiella pneumoniae isolate from a patient with meningitis and diabetes mellitus

BACKGROUND: Hypervirulent Klebsiella pneumoniae (hvKP) is an important cause of invasive community-acquired infection, particularly in individuals with diabetes mellitus. However, cerebrospinal fluid (CSF)-derived hvKP isolates, especially those belonging to the ST86-KL2 lineage, remain poorly characterized at the integrated clinical, genomic, and phenotypic levels. METHODS: A K. pneumoniae isolate, designated BP9811, was recovered from the CSF of a patient with meningitis and diabetes mellitus and identified by matrix-assisted laser desorption/ionization time-of-flight mass spectrometry and 16 S rRNA sequencing. Antimicrobial susceptibility testing and whole-genome sequencing were performed to define its resistance, virulence, sequence type (ST), capsular type, and plasmid content. Virulence was evaluated using the Galleria mellonella infection model. In addition, interaction with human cerebral microvascular endothelial cells was preliminarily assessed using adhesion, gentamicin protection, and transmission electron microscopy assays, together with measurement of relative ompA transcription by reverse transcription-quantitative polymerase chain reaction. Comparative phylogenetic analyses were performed using publicly available CSF-derived and KL2 K. pneumoniae genomes. RESULTS: BP9811 was identified as a hypermucoviscous ST86-KL2 hvKP isolate that remained susceptible to all tested antimicrobial agents. Whole-genome sequencing revealed an IncHI1B virulence plasmid carrying canonical hvKP-associated determinants, including rmpA/rmpA2, peg-344, iucABCD, and iroBCD. In the Galleria mellonella model, BP9811 showed high virulence comparable to that of the hypervirulent reference strain NTUH-2044. In HCMEC/D3 cells, BP9811 exhibited increased adhesion and intracellular recovery under the tested conditions, and transmission electron microscopy confirmed bacterial internalization. BP9811 also showed higher ompA transcript levels than the control strain. Phylogenetic analysis indicated that BP9811 was genetically distinct from currently available CSF-derived isolates and occupied a related branch within the KL2 population. CONCLUSIONS: This study provides an integrated clinical, genomic, and phenotypic characterization of BP9811, a CSF-derived ST86-KL2 hvKP isolate recovered from a patient with meningitis and diabetes mellitus. BP9811 carried a canonical hvKP virulence plasmid, displayed marked virulence-associated phenotypes, and showed enhanced interaction with human cerebral microvascular endothelial cells in vitro under the tested conditions. These findings expand the limited isolate-level evidence on central nervous system-associated hvKP and provide a basis for future comparative and mechanistic studies.