Platelet Activation and Aggregation Induced by Streptococcus bovis/Streptococcus equinus Complex.

Area of Science:

• Microbiology
• Immunology
• Cardiovascular Research

Background:

• The Streptococcus bovis/Streptococcus equinus complex (SBSEC) is a significant cause of infective endocarditis (IE).
• Bacterial activation and aggregation of platelets are crucial virulence mechanisms in IE pathogens.
• Limited research exists on SBSEC's interaction with platelets and the underlying mechanisms.

Purpose of the Study:

• To investigate the capacity of SBSEC isolates to induce platelet activation and aggregation.
• To elucidate the mechanisms involved in SBSEC-mediated platelet responses.
• To identify potential therapeutic targets for SBSEC-related IE.

Main Methods:

• Collected 26 SBSEC isolates from bacteremia cases.
• Studied platelet interactions using platelet-rich plasma (PRP) from human donors.
• Assessed aggregation via light-transmission aggregometry and activation via CD62P expression using flow cytometry.
• Utilized inhibitors and IgG cleavage to determine the role of Fc-receptors and IgG.

Main Results:

• Twenty-two of 26 SBSEC isolates induced platelet aggregation in at least one donor.
• Isolate SL1 demonstrated rapid aggregation (50% in 70s).
• Platelet activation and aggregation were abolished by blocking Fc-receptors or cleaving IgG, indicating an IgG-Fc-receptor dependent pathway.
• Bacteria-induced platelet aggregation was transferable via serum, suggesting soluble factors are involved.

Conclusions:

• SBSEC isolates commonly induce platelet aggregation, a host-dependent phenomenon.
• The IgG-Fc-receptor pathway is essential for SBSEC-mediated platelet activation and aggregation.
• This pathway represents a potential therapeutic target for preventing and treating IE caused by SBSEC.