Blood bacterial DNAemia is associated to serum zonulin level in older subjects

Background: Several studies in the last decade suggested the existence of a richmicrobiota in human bloodstream. Assuming that increased presence of bacteria inblood can represent a significant factor in the development and progression of agingassociated diseases, here we performed the quantification and the taxonomic profilingof the bacterial DNA in blood samples collected from a group of forty-four oldersubjects enrolled in a nursing home. Metabolic and functional markers were alsomeasured and used to evaluate possible associations with bacterial DNA.Results: qPCR analysis revealed that all the older volunteers harbored detectableamounts of bacterial DNA in their blood. 16S rRNA gene profiling showed that thebacterial DNA detected in blood was mostly ascribable to the Gram-negative phylumProteobacteria. Furthermore, whereas the taxonomic structure was quite similar (with apredominance of Pseudomonadaceae and Enterobacteriaceae), the total amount ofbacterial DNA varied considerably between subjects. Correlation analyses revealedthat the bacterial DNA detected in blood (both as overall DNA load and DNAconcentration of specific bacterial taxa) correlated with several host parameters thatare markers for intestinal permeability, immune response, kidney and liver function,and insulin sensitivity. Particularly, we found a significant correlation between theamount of circulating bacterial DNA and zonulin serum levels, an emerging marker ofintestinal permeability.Conclusions: In this study, we report for the first time that older individuals harbordetectable amounts of bacterial DNA in blood. The correlation with zonulin levelssuggests that para-cellular permeability of epithelial and endothelial cell layers mayplay an important role in bacterial migration into the bloodstream. These findings leadus to speculate that the bacterial DNA detected in blood is indicative of a bloodmicrobiota that may influence several aspects of host physiology as well as thedevelopment and prognosis of diseases in older subjects.