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Hypervirulent Klebsiella pneumoniae causing aortitis retains its capsule and mucoviscosity and remains genotypically

Thomas A Russo1,2,3,4,5, Ulrike Carlino-MacDonald6,7, Zachary J Drayer7

  • 1The Veterans Administration Western New York Healthcare System, 3495 Bailey Ave, Buffalo, NY, 14215, USA. trusso@buffalo.edu.

Scientific Reports
|November 13, 2025
PubMed

Insights

Hypervirulent Klebsiella pneumoniae (hvKp) caused aortitis. The capsule-positive, mucoviscous phenotype persisted during treatment, suggesting it’s crucial for infection survival and may require prolonged therapy with adjunctive treatments.

Area of Science:

  • Infectious Diseases
  • Microbiology
  • Vascular Surgery

Background:

  • Aortitis is a severe infection affecting the aorta.
  • Hypervirulent Klebsiella pneumoniae (hvKp) is an emerging pathogen causing invasive infections.
  • The role of hvKp virulence factors in systemic infections like aortitis is not fully understood.

Purpose of the Study:

  • To characterize hvKp isolates from a patient with aortitis.
  • To investigate the in vitro and in vivo stability of hvKp virulence factors during antimicrobial therapy.
  • To understand the role of capsular polysaccharide and mucoviscosity in hvKp pathogenesis.

Main Methods:

  • Genomic and phenotypic characterization of hvKp isolates.
  • In vitro studies of capsule-deficient mutants.
  • Assessment of bacterial resistance to phagocytosis and complement-mediated bactericidal activity.

Main Results:

  • The hvKp isolate remained genomically and phenotypically unchanged after prolonged antimicrobial therapy, retaining its capsule and mucoviscosity.
  • Capsule-deficient mutants were generated in vitro, but the capsule-positive phenotype was selected for in vivo.
  • Capsule-positive strains showed resistance to phagocytosis but increased sensitivity to complement-mediated killing compared to capsule-minus strains.

Conclusions:

  • The capsule-positive, mucoviscous phenotype of hvKp is stable and selected for during systemic infection.
  • Phagocytosis resistance is a key defense mechanism for hvKp in the systemic compartment.
  • Prolonged antimicrobial therapy and potential adjunctive treatments are likely necessary for hvKp aortitis.

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