Historically, human blood has long been thought of as microbe-free, apart from stray guests that occasionally enter the bloodstream through small cuts from accidents or daily activities like toothbrushing. However, advances in genomic technologies such as DNA sequencing and metagenomics are challenging this notion. Reports of trace amounts of microbial DNA found within the human bloodstream hint at a potential native microbiome, which—like those in our gut and on our skin—may play an important role in health and disease.
“Given the growing excitement about the presence of a blood microbiome, it was important to study the problem rigorously to help the scientific and medical community reach an informed consensus,” said Cedric Tan, an A*STAR National Science Scholar.
Seeking more concrete proof, a research team led by Niranjan Nagarajan, Senior Group Leader at A*STAR’s Genome Institute of Singapore (GIS), re-analysed sequencing data that had been generated in Phase I of Singapore’s 10-year National Precision Medicine Strategy, taking a closer look at microbial signatures in the blood of 9,770 healthy individuals.
Comprising Niranjan, Tan and colleagues from GIS and Nanyang Technological University, Singapore, the team implemented rigorous computational analyses to remove potential contaminants and ensure the robustness of their findings.
The results revealed a sporadic and random presence of microbes in the blood of healthy individuals, with no evidence of a structured microbial community, refuting recent claims of the presence of a blood microbiome. Of the 117 microbial species detected in the study, most originated from the gut, mouth and genitourinary microbiomes.
“This list of microbes is a valuable resource on the types of microorganisms that we expect to occasionally see in the blood of healthy individuals,” said Tan, adding that this newly-established baseline can be a significant tool in developing improved screening tests for blood donations.
Tan added that while the team’s research has provided insights into the microbial composition of blood in healthy people, further investigation is necessary. “Our findings do not exclude the possibility that there might be a more persistent community of blood microbes in patients with chronic diseases such as cancer, cardiovascular disease or diabetes,” said Tan, adding that the team plans to explore whether such communities exist and if they are linked to these conditions.
The A*STAR-affiliated researchers contributing to this research are from the Genome Institute of Singapore (GIS).
