Enterococcus faecalis endocarditis severity in rabbits is reduced by IgG Fabs interfering with aggregation substance

Area of Science:

• Microbiology
• Immunology
• Infectious Diseases

Background:

• Enterococcus faecalis is a primary cause of infective endocarditis.
• Enterococcal aggregation substance (AS) is a key virulence factor in endocarditis, promoting bacterial aggregation.
• Endocarditis can occur even without AS production.

Purpose of the Study:

• To evaluate the protective potential of antibodies against AS in a rabbit model of E. faecalis endocarditis.
• To investigate the role of IgG and its Fab fragments in AS-mediated virulence.

Main Methods:

• Active immunization of rabbits against AS+ or AS- E. faecalis.
• Passive administration of anti-AS IgG Fabs before bacterial challenge.
• Assessment of vegetation formation, microbial counts, and size in vivo.
• In vitro assays to measure bacterial aggregation.

Main Results:

• Active immunization against AS+ E. faecalis led to more severe vegetations and higher mortality compared to immunization against AS- E. faecalis.
• IgG antibodies against AS enhanced bacterial aggregation in vitro.
• Passive administration of anti-AS Fab fragments significantly reduced vegetation microbial counts and size.
• Anti-AS Fabs inhibited bacterial aggregation in vitro.

Conclusions:

• The study confirms AS's role in E. faecalis infective endocarditis.
• IgG antibodies against AS can exacerbate the disease by promoting aggregation.
• Anti-AS Fab fragments demonstrate therapeutic potential by preventing aggregation and reducing disease severity.