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Invasive Infection Caused by a Hypervirulent ST367-KL1 Klebsiella quasipneumoniae subsp. similipneumoniae: First Case

Shogo Saito1, Satoko Nakashima1, Kentaro Endo1

  • 1Department of Central Clinical Laboratory, Iwate Medical University Hospital, Japan.

Japanese Journal of Infectious Diseases
|July 1, 2026
PubMed

Insights

This study reports the first invasive infection by hypervirulent Klebsiella quasipneumoniae subsp. similipneumoniae in Japan. Whole-genome sequencing confirmed the pathogen, highlighting the need for advanced diagnostics and surveillance.

Area of Science:

  • Microbiology
  • Infectious Diseases
  • Genomics

Background:

  • Klebsiella quasipneumoniae is challenging to differentiate from K. pneumoniae using standard methods.
  • Limited data exists on the clinical presentation of K. quasipneumoniae infections.

Purpose of the Study:

  • To report the first case of invasive infection by hypervirulent K. quasipneumoniae subsp. similipneumoniae in Japan.
  • To emphasize the utility of whole-genome sequencing for accurate pathogen identification.
  • To underscore the importance of surveillance for emerging pathogens.

Main Methods:

  • Case report of a patient with invasive infection.
  • Identification of the pathogen using conventional methods and whole-genome sequencing (WGS).
  • Analysis of virulence factors and antimicrobial susceptibility.

Main Results:

  • A 65-year-old female patient presented with liver abscess and pulmonary nodules.
  • WGS identified the causative agent as K. quasipneumoniae subsp. similipneumoniae (ST367, KL1), exhibiting hypervirulence.
  • The patient successfully responded to meropenem and cefmetazole treatment.

Conclusions:

  • Hypervirulent K. quasipneumoniae can cause severe invasive infections.
  • WGS is crucial for precise identification of K. quasipneumoniae complex members.
  • Continuous clinical and genomic surveillance is necessary to track this emerging pathogen.
Keywords:
KL1Klebsiella quasipneumoniae subsp. similipneumoniaeST367hypervirulenceliver abscess

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