Fig. 2

Human neutrophils induce loss of SpeB in GAS. A Assessment of SpeB positivity/negativity of indicated strains via casein agar assay. Mean percentage from four independent experiments is shown (n = 4). B Representative image of Western-Blot analyses (n = 3; mSpeB, mature SpeB) and (C) SpeB activity assay (n = 3) of bacterial supernatants. GAS were grown over-night (16 h) in THY and sterile-filtered supernatants were used for the analyses. Original blot is shown in Additional file 1: Fig. S8. Each dot in C represents one independent experiment. Bars denote mean values ± SD. D Intracellular bacterial counts after 1 h of neutrophil infection. Each dot represents an experiment with neutrophils from one donor. The horizontal lines denote median values (n = 5). The level of significance was determined using Kruskal–Wallis test with Dunn’s multiple comparison post-test. E Assessment of SpeB positivity/negativity of indicated strains recovered from primary human neutrophils shown in D. Mean percentage of SpeB⁺ and SpeB⁻ clones from five independent experiments are shown (n = 5). Bacteria incubated in RPMI and THY media served as controls. F Distribution of SpeB⁺ and SpeB⁻ clones post neutrophil (PMN) and subsequent THY media passage. Displayed are mean [%] of five independent experiments (n = 5)