No evidence for a common blood microbiome based on a population study of 9,770 healthy humans

A large population study indicates that there is no core blood microbiome in healthy humans. Human blood is conventionally considered sterile but recent studies suggest the presence of a blood microbiome in healthy individuals. Here we characterized the DNA signatures of microbes in the blood of 9,770 healthy individuals using sequencing data from multiple cohorts. After filtering for contaminants, we identified 117 microbial species in blood, some of which had DNA signatures of microbial replication. They were primarily commensals associated with the gut (n = 40), mouth (n = 32) and genitourinary tract (n = 18), and were distinct from pathogens detected in hospital blood cultures. No species were detected in 84% of individuals, while the remainder only had a median of one species. Less than 5% of individuals shared the same species, no co-occurrence patterns between different species were observed and no associations between host phenotypes and microbes were found. Overall, these results do not support the hypothesis of a consistent core microbiome endogenous to human blood. Rather, our findings support the transient and sporadic translocation of commensal microbes from other body sites into the bloodstream.

Automated summary

A large-scale population study reveals that there is no consistent core blood microbiome in healthy individuals. While human blood is generally considered sterile, recent research suggests the presence of a blood microbiome in healthy people. After analyzing sequencing data from multiple cohorts, researchers identified 117 microbial species in the blood of 9,770 healthy individuals, primarily commensals associated with the gut, mouth, and genitourinary tract. However, no co-occurrence patterns or associations between host phenotypes and microbes were found, suggesting that the translocation of commensal microbes from other body sites into the bloodstream is transient and sporadic.