Serial Blood Microbiome Profiles in Kidney Transplant Recipients: Evidence of Circulating Gut Bacteria

Innovation in sequencing techniques has enabled the identification of microbiome in low biomass sites. In this study, we sought to investigate the utility of 16S rRNA deep sequencing of whole blood in kidney transplant recipients and to assess a link between the gut microbiota and the blood microbiota. We recruited 63 kidney transplant recipients who provided 163 whole blood specimens over the first 140 days after transplantation. We profiled the blood microbiome using 16S rRNA gene sequencing of the V4-V5 hypervariable region and additionally evaluated the gut microbiota in a subset of kidney transplant recipients who had gut bacteria detected in the blood. We generated a median of 19,959 sequences per blood specimen and found that most whole blood microbiome profiles consisted of mitochondrial DNA. While we did not identify classically pathogenic bacteria in the blood such as Escherichia, Klebsiella, and Enterococcus, we identified 25 gut bacterial taxa at very low levels in the blood of 22 kidney transplant recipients. For 9 of these kidney transplant recipients the same bacterial taxa detected in the blood were also identified in the gut microbiota. Our study is one of the first to show the detection of gut bacterial DNA in the blood of kidney transplant patients.