Association of blood microbiome composition with four diseases and five-year mortality

For decades blood has been considered as microbiologically sterile environment. However small number of researchers have also reported that microbes are found in the blood of apparently healthy individuals, but, because of high contamination probability, these reports were often dismissed as artefacts. Recent massive parallel sequencing and quantitation-based studies, which involved careful control of whole procedural pipeline, clearly demonstrated that bacterial DNA can indeed be found in the blood of both healthy and diseased humans and its primary sources are intestinal tract, mouth and skin. The recent findings in this field indicate that the alterations in blood microbial population structure are significantly associated with various diseases. In this study we performed 16S rRNA V3-V4 region sequencing combined with digital PCR on blood samples that were acquired from participants that have suffered from hepatitis C virus infection and cardiovascular diseases, are suffering from autoimmune diseases and colorectal cancer or died within five years after sample collection. Acquired results revealed that both blood microbiome alpha diversity and bacterial 16S rRNA gene concentration within blood of cancer patients significantly differed from that of healthy individuals and individuals that suffered from other studied diseases.