Protective role of complement in experimental Escherichia coli endocarditis

Area of Science:

• Microbiology
• Immunology
• Pathogenesis

Background:

• Infective endocarditis is a serious infection, typically caused by Gram-positive bacteria.
• The role of Gram-negative bacteria, like Escherichia coli, in endocarditis is less understood.
• Bacterial resistance to serum complement is a potential virulence factor.

Purpose of the Study:

• To investigate the role of serum resistance in the pathogenesis of experimental Escherichia coli endocarditis.
• To determine if serum sensitivity influences the ability of E. coli to establish persistent infection in the heart.

Main Methods:

• Fourteen strains of Escherichia coli were tested for their ability to cause endocarditis in rabbits with intracardiac catheters.
• Bacterial survival and infection rates were assessed in normal and C6-deficient rabbits.
• Serum bactericidal activity was evaluated for each E. coli strain.

Main Results:

• Serum-resistant E. coli strains caused endocarditis in 91.4% of rabbits, while serum-sensitive strains infected only 11.3%.
• Serum-sensitive E. coli survived less than 24 hours in normal rabbits but caused endocarditis in all C6-deficient rabbits.
• No correlation was observed between K1 antigen presence and endocarditis incidence.

Conclusions:

• Resistance to complement-mediated serum bactericidal activity is directly associated with the ability of E. coli to cause persistent endocardial infection.
• These findings may explain the rarity of Gram-negative bacterial endocarditis and underscore the importance of the serum bactericidal system in host defense.