FIGURE 2.

(a) Saponin 0.0125% induces human cell lysis, without inducing bacterial cell lysis. The effect of Triton and saponin on bacterial cell lysis was measured. This experiment was performed for Streptococcus gallolyticus (Firmicutes), Bacteroides vulgatus (Bacteroidetes), Escherichia coli (γ‐Proteobacteria), and Collinsella intestinales (Actinobacteria). The ratio between the concentration in treated versus untreated (PBS) was plotted. An increase of more than 2 was considered relevant. Results show that Triton affects bacterial cell lysis in Streptococcus gallolyticus and Bacteroides vulgatus, but not in Escherichia coli and Collinsella intestinalis. Saponin only induced cell lysis at 0.1% in E. coli. (b) Biopsies were isolated with strategy 2 in combination with Triton (Trit) and saponin (Sap) at different concentrations. The relative bacterial signal for Firmicutes, Bacteroidetes, Actinobacteria, and γ‐Proteobacteria was calibrated with the universal 16S rRNA signal (ΔCt) and was compared to PBS (ΔΔCt). Similarity to PBS was calculated through ranking using the Friedman test. Both saponin concentrations most closely resembled bacterial composition in PBS and hence preserved bacterial composition at phylum level in the colon biopsies. (c) DNA release of biopsies was measured after exposure to either PBS or saponin 0.0125%. More external DNA (eDNA) was measured after incubation with saponin 0.0125% (p = 0.05), suggesting that human cell lysis was induced, although eDNA was also detected in the sample with PBS alone