„Non-toxic“ S. aureus strains and CoNS S. epidermidis induce IL1-ß after phagocytosis
Previously, killing within macrophages was linked to inflammasome activation (Cohen et al., 2018; Muller et al., 2015; Shimada et al., 2010; Sokolovska et al., 2013). We questioned whether „non-toxic“S. aureus was still able to provoke IL-1ß release as read-out for inflammasome activation. Since there are also major differences betweenS. aureus strains (Pidwill et al. , 2021), we included anagr/sae mutant of strain Newman into the analysis. There was no significant difference between bacterial survival or cytotoxicity of „non-toxic“ USA300 versus „non-toxic“ strain Newman (Fig. 2A, 2B). Interestingly, IL-1ß was detectable not only in cells infected with the „non-toxic“ S. aureus strains but also in those infected withS. epidermidis (Fig. 2C). IL-1ß release indicates that intracellular S. aureus as well as CoNS induce inflammasome activation. However, since there is no significant difference between species, inflammasome activation doesn’t account for the differences observed in bacterial survival. We next tested bacterial survival, cytotoxicity and IL-1ß release in human primary macrophages (hMDM). Again CoNS S. epidermidis was more efficiently killed compared to „non-toxic“ S. aureus (Fig. 2D). IL-ß release was not significantly different between species (Fig. 2F).