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In Vivo Evolution of a Klebsiella pneumoniae Capsule Defect With wcaJ Mutation Promotes Complement-Mediated
William Bain1,2, Brian Ahn3, Hernán F Peñaloza1
1Division of Pulmonary, Allergy, Critical Care, and Sleep Medicine, Department of Medicine, University of Pittsburgh.
Background:
Klebsiella pneumoniae carbapenemase-producing K pneumoniae (KPC-Kp) bloodstream infections are associated with high mortality. We studied clinical bloodstream KPC-Kp isolates to investigate mechanisms of resistance to complement, a key host defense against bloodstream infection.
Methods:
We tested growth of KPC-Kp isolates in human serum. In serial isolates from a single patient, we performed whole genome sequencing and tested for complement resistance and binding by mixing study, direct enzyme-linked immunosorbent assay, flow cytometry, and electron microscopy. We utilized an isogenic deletion mutant in phagocytosis assays and an acute lung infection model.
Results:
We found serum resistance in 16 of 59 (27%) KPC-Kp clinical bloodstream isolates. In 5 genetically related bloodstream isolates from a single patient, we noted a loss-of-function mutation in the capsule biosynthesis gene, wcaJ. Disruption of wcaJ was associated with decreased polysaccharide capsule, resistance to complement-mediated killing, and surprisingly, increased binding of complement proteins. Furthermore, an isogenic wcaJ deletion mutant exhibited increased opsonophagocytosis in vitro and impaired in vivo control in the lung after airspace macrophage depletion in mice.
Conclusions:
Loss of function in wcaJ led to increased complement resistance, complement binding, and opsonophagocytosis, which may promote KPC-Kp persistence by enabling coexistence of increased bloodstream fitness and reduced tissue virulence.
Insights
Loss of capsule gene wcaJ in Klebsiella pneumoniae increases resistance to complement, aiding bloodstream infection survival. This mutation enhances complement binding and opsonophagocytosis, impacting virulence.
Area of Science:
- Microbiology
- Immunology
- Infectious Diseases
Background:
- Klebsiella pneumoniae carbapenemase-producing K pneumoniae (KPC-Kp) bloodstream infections are a significant cause of mortality.
- Complement is a critical host defense mechanism against bloodstream infections.
Purpose of the Study:
- To investigate the mechanisms of complement resistance in clinical KPC-Kp isolates.
- To understand how KPC-Kp evades complement-mediated killing during bloodstream infections.
Main Methods:
- Growth of KPC-Kp isolates in human serum was assessed.
- Whole genome sequencing was performed on serial isolates from a single patient.
- Complement resistance, binding, opsonophagocytosis, and in vivo infection models were utilized.
Main Results:
- Serum resistance was observed in 27% of KPC-Kp isolates.
- A loss-of-function mutation in the wcaJ gene was identified in genetically related isolates.
- wcaJ disruption decreased capsule, increased complement resistance and binding, and enhanced opsonophagocytosis.
Conclusions:
- Loss of wcaJ function enhances complement resistance and binding, potentially promoting KPC-Kp persistence.
- The findings suggest a trade-off between bloodstream fitness and tissue virulence.
- Targeting capsule biosynthesis could be a strategy to combat KPC-Kp infections.
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