Pigmented GBS activate and kill human platelets. Washed human platelets were infected with the pigmented LUMC16 and the non-pigmented LUMC16ΔcylX-K GBS strains at MOI 0.1, MOI 1.0, and MOI 10. (A) Platelet activation was measured via flow cytometry using a PE-Cy5 labelled CD62P antibody. TRAP-6 (40 µM) and PBS were used as positive and negative controls, respectively. Alternatively, 5 min prior to the end of infection, TRAP-6 (40 µM) was added. The activation process was evaluated by assessing frequencies of CD62P-positive cells (A) as well as expression of CD62P (B). Each dot in A and B represents one independent experiment with washed platelets from one donor (n = 4). Horizontal lines depict mean values. (C) Kinetics of platelet viability. PBS and TritonX-100 were used as controls. Each dot represents the mean ± SD from four independent experiments (n = 4). Abbreviations (GMFI, geometric mean of fluorescence intensity; RLU, relative luminescence units).