Intestinal inflammation leads to changes in the blood PBMC and plasma microbiome

Despite several studies having confirmed the presence of bacteria in the blood of humans, very little is known about the distribution of microbial DNA among leukocytes in the systemic circulation. In this preliminary study, we aimed 1) to evaluate the peripheral blood mononuclear cells (PBMC) and plasma bacterial microbiome in humans, and 2) to investigate potential bacterial translocation into systemic circulation. To address these questions, two groups of individuals were selected for the microbiome analyses of both plasma and PBMC samples: one group with acute intestinal inflammation and the other without it. Along with several blanks and microbial community standards, the DNA was extracted from the plasma and PBMC samples using the Ultra-Deep Microbiome Prep Kit from Molzym. Then, 16S v3v4 amplicon libraries were made using the standard NexteraXT Illumina library prep protocol and sequenced on a MiSeq v3 platform. After careful contaminant removal, sequences were analyzed using the Qiime2 pipeline. We found that patients with intestinal inflammation are more likely to have detectable bacterial microflora than those without it, moreover, the bacterial composition of the two groups was significantly different from each other. Enterococcus faecalis and Escherichia-Shigella genus, bacteria more likely to originate from the intestine, were enriched in the group with intestinal inflammation in both plasma and PBMC. The result was confirmed by PCR. Due to the preliminary feature of the study, the main limitations are the small sample size and lack of correction for potential cofounders. The measurement of the microbiome from plasma and PBMC may provide a new method for the characterization of intestinal inflammation and offer a new diagnostic and therapeutic target.