Related Experiment Video
Updated: Jan 20, 2026
Microaerobic Fermentation of Bamboo Hydrolysate by Klebsiella pneumoniae
Published on: November 28, 2025
Complement mediated Klebsiella pneumoniae capsule changes
Trine S Jensen1, Katharina V Opstrup1, Gunna Christiansen2
1Department of Health Science and Technology, Aalborg University, Fredrik Bajers Vej 3b, 9220, Aalborg, Denmark.
Abstract:
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.
Insights
Multidrug-resistant Klebsiella pneumoniae infections are a growing threat. This study reveals how the bacterium
Area of Science:
- Microbiology
- Immunology
- Infectious Diseases
Background:
- Klebsiella pneumoniae is an opportunistic pathogen causing severe infections like sepsis.
- Multidrug resistance in K. pneumoniae complicates treatment and increases mortality.
- Understanding host-pathogen interactions is crucial for developing new therapies.
Purpose of the Study:
- To investigate the interaction between clinical K. pneumoniae isolates and human serum.
- To elucidate mechanisms of immune evasion by K. pneumoniae.
- To determine how complement activation affects K. pneumoniae capsule structure.
Main Methods:
- Characterization of ten clinical K. pneumoniae isolates from bacteremia patients.
- Investigation of isolate interactions with human serum.
- Analysis of complement activation pathways and deposition.
- Morphological analysis of bacterial capsules and outer membranes.
Main Results:
- All K. pneumoniae isolates activated the alternative complement pathway.
- Seven isolates exhibited serum resistance, with complement deposition in their capsules.
- Capsule changes and shedding were observed in serum-resistant isolates, preventing lysis.
- One serum-sensitive isolate showed complement activation across multiple pathways, leading to lysis and membrane attack complex formation.
Conclusions:
- The capsule of serum-resistant K. pneumoniae acts as a defense mechanism against complement-mediated lysis.
- K. pneumoniae employs capsule modifications to evade host immune responses.
- Targeting capsule-complement interactions may offer novel therapeutic strategies against K. pneumoniae infections.
Related Concept Videos
03:14Microaerobic Fermentation of Bamboo Hydrolysate by Klebsiella pneumoniae
07:24Production of Chemicals by Klebsiella pneumoniae Using Bamboo Hydrolysate as Feedstock
05:52Separating Bacteria by Capsule Amount Using a Discontinuous Density Gradient
09:49Experimental Model to Evaluate Resolution of Pneumonia
05:40A Serum Bactericidal Assay for the Complement-Mediated Bactericidal Activity of Antibodies
01:27Complement System