Ratio of bacteria to macrophages in microscopic analysis and response of THP-1 macrophages to Streptococcus gallolyticus subsp. gallolyticus strains and Staphylococcus aureus ATCC 25923.

1+2) Microscopic analysis revealed the ratio of bacteria counted (without differentiation between dead and alive bacteria) to macrophages with the distinction between bacteria within and outside macrophages (bacteria/macrophage; counted macrophages are set as 1; Fig A and supplemental method in S1 File; n = 100 macrophages). 3) The oxidative reaction of macrophages to bacteria was detected by fluorescence signaling (DCF) at time point t = 0 h. H2O2 (1 mM) was used as stimulation control (Fig B1 in S1 File). 3) Cytotoxicity of bacteria to THP-1 macrophages compared to control (lysis of THP-1 macrophages by lysis buffer was set as 100%) was analyzed by LDH-assay 5 h after phagocytosis (Fig B2 in S1 File). 4–6) Gene expression of cytokines in THP-1 macrophages was determined by real-time PCR after stimulation with the different bacteria (t = 5 h); the control without bacterial stimulation was set as one (Fig C in S1 File). Results of statistical analysis (Mann-Whitney U test) of individual strains are arranged in tabular form. Only significant differences between strains and bacterial species are represented. Arbitrary units = au; SA = Staphylococcus aureus; bac = bacterial cells; I = intracellular; e = extracellular; m = macrophage; n = 3.