Phenotype and molecular characterization of K1-ST700 hypervirulent Klebsiella pneumoniae isolated from bone marrow aspirate of a patient with multi-system infection

BACKGROUND: Worldwide, hypervirulent Klebsiella. pneumoniae (HvKp) is a leading cause of multisystem infection. However, it is very rare for HvKp to be cultured from bone marrow aspirates. In this study, four K1-ST700 Klebsiella pneumoniae (K. pneumoniae) isolates were acquired from the bone marrow, blood, liver abscess puncture fluid, and bronchoalveolar lavage fluid (BALF) of a 53-year-old male patient in a Chinese hospital. The patient rapidly developed fatal multiple-organ failure caused by K1-ST700 HvKp infection. METHODS: Isolates were determined as K. pneumoniae via the VITEK-2 Compact system and validated by the VITEK-MS system. Antimicrobial susceptibility assessment of four isolates was conducted via the VITEK-2 Compact system. MLST of K. pneumoniae was conducted following the Pasteur Institute protocol. The virulence of isolates was detected through serotype and mouse lethality assay. The bone marrow isolate (KPN-BM) underwent whole-genome sequencing and was compared to available K1 K. pneumoniae genomes from China. RESULTS: All isolates exhibited high virulence in a mouse infection model and remained susceptible to all tested antibiotics. The complete genome sequence was deposited in GenBank (accession no. JBRNXP000000000). A total of 133 virulence-associated genes were identified in KPN-BM, including genes involved in iron acquisition, immune evasion, bacterial adherence, and type VI secretion. A total of 64 K. pneumoniae isolates of K1 reported in China exhibited stable phylogenetic relationships. Fifty-eight strains belong to the ST23 type. Five K1-ST700 K. pneumoniae strains from China and Norway carry similar virulence genes. CONCLUSIONS: K1-ST700 HvKp may represent an emerging high virulence clone with the potential for transmission. HvKp-induced bone marrow infection is very rare and should be given clinical attention.