Background: Streptococcus pneumoniaeis a human pathogen causing serious health issues including community-acquired pneumonia and pneumonia induced acute respiratory distress syndrome (ARDS). Recent studies have shown that platelets are important players in infection processes and influence the growth of pathogenic bacteria.

Aims: Investigation of the interplay of platelets and different S. pneumoniae serotypes.

Methods: Platelets were isolated from blood of healthy donors (n≥3). Pneumococcal serotypes 2 (D39), 4 (TIGR4), 6B and 19F and pneumolysindeficient mutants (D39Dply; TIGR4Dply) were grown in complex THY-Medium to mid-exponential phase. Platelets, releasates of activated platelets (stimulated with 5µg/ml collagen, 20µM TRAP-6)and platelet lysates were incubated at a ratio of 5 platelets per S. pneumoniaefor 2, 3 or 4 hours. Colony forming units (CFU) were determined. Platelet activation was analyzed by CD62P expression using flow cytometry.

Results: All four wildtype strains induced CD62P expression on platelets (positive cells ≥29%). Pneumolysin deficient mutants caused only moderate CD62P expression (positive cells ≥7%) and subsequent TRAP-6 stimulation further increased activation at all conditions tested (Fig.1).Platelets did notinfluence growth of strains D39 (wildtype and plymutant), 6B and 19F while growth of TIGR4 was significantly affected. (Fig.2a: p=0.002 (2h)). Living platelets (p=0.0001 (4h)) and platelet lysate (p=0.0001 (4h)) inhibited bacterial growth, while platelet releasate had no effect (Fig.2b).

Conclusions: The interaction between platelets and S. pneumoniaeseems to be strain specific with a dominant role of pneumolysin. Interestingly, growth of S. pneumoniaecan be inhibited by whole platelets and platelet lysates but not by supernatant of activated platelets (releasate) indicating that the inhibition of S. pneumoniae growth is not mediated by components stored in the platelet granules but rather in the cytoplasm.

[Fig.1: CD62P expression on platelets after incubation with different S. pneumonia strains]

[Fig.2: Influence of platelets and platelet components on the growth of different S. pneumonia strains]

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ISTH Congress Abstracts - https://abstracts.isth.org/abstract/interaction-between-platelets-and-streptococcus-pneumoniae/