Fig. 2

Absolute levels of bacterial DNA from saliva, stool and plasma. A droplet digital PCR (ddPCR) targeting the V4 region of the 16S rRNA gene was used to measure the absolute levels of all bacterial DNA from different biospecimen sources. A The levels of bacterial DNA are shown for a subset of 10 stool, 4 saliva and 58 plasma samples collected in the study and a subset of 12, 4 and 40 DNA Extraction Negative Controls (DENCs) corresponding to each sample-type, respectively. For DENCs, nuclease-free water was the only input used for the DNA extraction. Levels are also shown for 28 replicates of a non-template control (NTC) where nuclease-free water was the only input used for the ddPCR reaction. The sample to DENC median ratio for saliva, stool and plasma were 2064, 2919, and 1.43, respectively. The plasma-DENC to saliva-DENC and stool-DENC ratio were 8.23 and 6.77, respectively. B The concentration levels of microbial DNA in plasma are shown for each individual DNA extraction batch (DEB) together with their corresponding DENCs. The number of plasma samples tested for DEB A-E was 15, 10, 14, 11 and 8, respectively. The number of plasma-DENC replicates tested for DEB A-E was 9, 9, 8, 8 and 6 respectively. The plasma to DENC median ratio for DEBs A to E, were 1.62, 1.2, 1.84, 1.34 and 1.6, respectively. Statistical significance for differences between groups was determined by generalised estimating equations (GEE) test; *** p < 0.001, ns-not significant