Abstract:
The blood that flows perpetually through our veins and arteries performs numerous
functions essential to our survival. Besides distributing oxygen, this vast circulatory
system facilitates nutrient transport, deters infection and dispenses heat throughout
our bodies. Since human blood has traditionally been considered to be an entirely
sterile environment, comprising only blood-cells, platelets and plasma, the detection
of microbes in blood was consistently interpreted as an indication of infection.
However, although a contentious concept, evidence for the existence of a healthy
human blood-microbiome is steadily accumulating. While the origins, identities and
functions of these unanticipated micro-organisms remain to be elucidated, information
on blood-borne microbial phylogeny is gradually increasing. Given recent advances in
microbial-hematology, we review current literature concerning the composition and origin
of the human blood-microbiome, focusing on bacteria and their role in the configuration
of both the diseased and healthy human blood-microbiomes. Specifically, we explore
the ways in which dysbiosis in the supposedly innocuous blood-borne bacterial
microbiome may stimulate pathogenesis. In addition to exploring the relationship
between blood-borne bacteria and the development of complex disorders, we also
address the matter of contamination, citing the influence of contaminants on the
interpretation of blood-derived microbial datasets and urging the routine analysis
of laboratory controls to ascertain the taxonomic and metabolic characteristics of
environmentally-derived contaminant-taxa.
