Cultural Isolation and Characteristics of the Blood Microbiome of Healthy Individuals

Abstract

Background: On the analogy of the non-pathogenic microbiota found in oral cavity, skin and gastrointestinal tract, existence of blood microbiota was confirmed by DNA sequencing, but never deeply characterized. Hypothesis for the existence of dormant blood microbiota in healthy humans have been arisen and single species have been isolated. The aim of our study was to resuscitate and investigate the biodiversity of bacterial and fungal dormant blood microbiota in healthy individuals by blood culturing and NGS DNA sequencing. Results: Twenty eight blood samples of healthy individuals, seven for each blood type, were studied. Several culture media were tested. Blood microbiota resuscitation was performed in BHI broth supplemented with vitamin K 1 mg/ml, 2% sucrose, 0.25% sodium citrate and 0.2% yeastolate at 43˚C for 72 h. All tested blood samples were culture positive, as confirmed by Gram staining and TEM. TEM images demonstrated well defined cell structures. Analysis for bacterial and eukaryotic species was performed by 16S rRNA and ITS2 targeted sequencing. The obtained sequences were clustered (≥97% identity) in Operational Taxonomic Units (OTUs). Among cultured and uncultured samples we identified OTUs similarity with 47 bacterial orders belonging to 15 phyla and 39 fungi orders blonging to 2 phyla. For the first time we demonstrated isolation and sequencing identification of fungal blood microbiota in healthy individuals. Blood-group differences were identified among the bacterial microbiome compositions. Conclusion: The dormant blood microbiome is innate of the healthy individuals. Interventional strategies to bind the host blood microbiome with the states of health and disease remain an unmet research goal.

Multi-Method Characterization of the Human Circulating Microbiome

“…Negative cultures were repeated on two further occasions to confirm this status. These results are relatively consistent with previous studies, whereby 2–100% of blood samples were positive for bacterial growth (Wilson et al, 1975; Domingue and Schlegel, 1977; Jiménez et al, 2005; Damgaard et al, 2015; Panaiotov, 2018). Unexpectedly, bacterial growth was observed in aerobic conditions for all culture-positive blood samples, but anaerobic growth was only observed for four of the culture-positive blood samples.…”

Multi-Method Characterisation of the Human Circulating Microbiome

“…Bacterial cultures were positive for 80% of blood samples assayed (8 out of 10 samples; 4 control blood samples and 4 asthma blood samples), whilst all negative control plates had no growth as expected. These results are relatively consistent with previous studies, whereby 2-100% of blood samples were positive for bacterial growth 18, 54-57 . Unexpectedly, bacterial growth was observed in aerobic conditions for all culture-positive blood samples, but anaerobic growth was only observed for four of the culture-positive blood samples.…”

The Healthy Human Blood Microbiome: Fact or Fiction?

“…The fungal microbiomes of the human intestinal tract, mouth, skin, lungs, and other body-sites have been explored (Cui et al, 2013; Huffnagle and Noverr, 2013). As the presence of fungi in the blood of healthy individuals has only recently been reported (Panaiotov et al, 2018), more research concerning the human blood myco-biome, in particular studies including stringent negative controls, is required. Regarding a tentative human blood-virome, and following the exclusion of taxa attributable to contamination, Moustafa et al (2017) recovered 19 viral taxa from 42% of overtly non-diseased individuals.…”

“…Timeline indicating significant advances concerning HBM research. Images modified from Pease (1970), Domingue and Schlegel (1977), Bessis and Delpech (1981), McLaughlin et al (2002), and Panaiotov et al (2018). …”