Biofilm-dispersed pneumococci induce elevated leukocyte and platelet activation

Area of Science:

• Microbiology
• Immunology
• Pathogenesis

Background:

• *Streptococcus pneumoniae* colonizes the nasopharynx and can cause invasive diseases like pneumonia and sepsis.
• *Streptococcus pneumoniae* exhibits distinct phenotypes when grown as biofilms versus in planktonic culture.
• The interaction of niche-adapted pneumococcal populations with immune cells in the vascular compartment is poorly understood.

Purpose of the Study:

• To investigate the activation of neutrophils, monocytes, and platelets by different *Streptococcus pneumoniae* populations.
• To compare the immune response to biofilm bacteria, dispersed bacteria, and planktonic bacteria.
• To understand how *Streptococcus pneumoniae* interacts with key immune cells during infection.

Main Methods:

• *Ex vivo* stimulation of whole blood and platelet-rich plasma with *Streptococcus pneumoniae* populations.
• Flow cytometry and ELISA were used to measure immune cell activation markers.
• Assessment of platelet-neutrophil and platelet-monocyte complex formation and platelet responsiveness.

Main Results:

• Biofilm-derived bacteria (biofilm and dispersed) induced significant activation of neutrophils, monocytes, and platelets.
• Planktonic bacteria induced minimal immune cell activation.
• Platelets remained functional post-stimulation, with responsiveness inversely related to initial activation; bacterial association with immune cells mirrored activation patterns.

Conclusions:

• *Streptococcus pneumoniae* populations derived from biofilms elicit a robust immune response involving neutrophils, monocytes, and platelets.
• The distinct immune interactions of biofilm-derived bacteria compared to planktonic bacteria may be critical for disease development.
• Understanding these interactions could identify novel immunomodulatory therapeutic targets for pneumococcal infections.