Complement mediated Klebsiella pneumoniae capsule changes

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  • Trine S. Jensen, University of Aalborg, Denmark
  • Katharina V. Opstrup, University of Aalborg
  • ,
  • Gunna Christiansen
  • Pernille Vigsø Rasmussen, University of Southern Denmark, University of Aalborg, Denmark
  • Mikkel E. Thomsen, University of Aalborg
  • ,
  • Daniel L. Justesen, University of Aalborg
  • ,
  • Henrik C. Schønheyder
  • Mads Lausen, University of Aalborg
  • ,
  • Svend Birkelund, University of Aalborg

The Gram-negative bacterium Klebsiella pneumoniae is an opportunistic pathogen, which can cause life-threatening infections such as sepsis. Worldwide, emerging multidrug resistant K. pneumoniae infections are challenging to treat, hence leading to increased mortality. Therefore, understanding the interactions between K. pneumoniae and the immune system is important to develop new treatment options. We characterized ten clinical K. pneumoniae isolates obtained from blood of bacteremia patients. The interaction of the isolates with human serum was investigated to elucidate how K. pneumoniae escapes the host immune system, and how complement activation by K. pneumoniae changed the capsule structure. All K. pneumoniae isolates activated the alternative complement pathway despite serum resistance of seven isolates. One serum sensitive isolate activated two or all three pathways, and this isolate was lysed and had numerous membrane attack complexes in the outer membrane. However, we also found deposition of complement components in the capsule of serum resistant isolates resulting in morphological capsule changes and capsule shedding. These bacteria did not lyse, and no membrane attack complex was observed despite deposition of C5b-9 within the capsule, indicating that the capsule of serum resistant K. pneumoniae isolates is a defense mechanism against complement-mediated lysis.

Original languageEnglish
JournalMicrobes and Infection
Volume22
Issue1
Pages (from-to)19-30
Number of pages12
ISSN1286-4579
DOIs
Publication statusPublished - Jan 2020

    Research areas

  • Bacterial capsules, Complement system, Klebsiella pneumoniae, Membrane attack complex, Serum resistance

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