Identification of the composition, stability, and origin of blood microbiome in humans

Abstract BackgroundAn increasing number of research studies observe that human blood is not a completely sterile environment and has its own representative microbiome. This study aimed to determine the blood microbiome's composition, potential origin, and dynamics in humans.ResultsTo detect the origin of exogenous bacterial nucleic acids in the blood, we determined taxonomic composition based on 16S rRNA gene analysis in samples obtained from skin, vaginal, oral, and faecal swabs along with whole blood samples in a group of 10 volunteers. We observed a presence of bacterial DNA with variable taxonomic composition in all blood samples strongly dominated by members of the Pseudomonas genus. In addition, we detected identical bacterial Amplicon Sequence Variants (ASV) that overlapped between blood and other locations in all participants. Overall, 27.4% median of all ASVs from blood were also found in various locations, with the highest number found in the samples collected from skin swabs. Overall, 25.3% of the ASV found in blood overlapped between the baseline and three-month blood samples, indicating the blood microbiome's relative stability.ConclusionsWe have presented for the first time a remarkable overlap between the bacterial composition of blood and other locations of the same individuals, allowing us to propose the skin microbiota as the primary source of blood-related exogenous DNA. Furthermore, our results add a piece of new knowledge on the stability of the blood microbiome, providing the basis for future studies to identify the potential effect of the blood microbiome on the phenotype or disease.