Blood microbiome of patients with atherosclerosis

Aim of the study was to assess the composition of blood microbiome in patients with atherosclerosis, to compare it with microflora and microbiome of atherosclerotic plaques, to identify common taxons for microbiomes of blood and atherosclerotic plaques, as well as to perform a correlation analysis of various blood and urine parameters in the examined patients with the structure of «core» of the blood bacterial community. 
Material and methods. 19 men and 5 women aged 33–81 years (mean age 64.1 ± 9.8 years) with common carotid artery atherosclerosis confirmed by Doppler ultrasonography of vessels were examined. The microbial diversity of 24 blood samples from patients with vascular atherosclerosis was examined using 16S ribosomal RNA (16S rRNA) gene sequencing. 16 samples of atherosclerotic carotid artery plaques were examined by а bacteriological method. Correlation analysis of the results was performed by methods of nonparametric statistics. 
Results. Most of the sequences obtained were classified as Proteobacteria (73.9 %), Actinobacteria (11.4 %), Bacteroidetes (2.8 %), Cyanobacteria (1.3 %), Firmicutes (1.1 %), Fusobacteria (0.7 %). Genes of 16S rRNA of Propionibacterium acnes, undifferentiated species of the families Micrococcaceae, Caulobacteraceae, Bradyrhizobiaceae, genera Bradyrhizobium and Sphingomonas were found in all the examined blood samples of patients with atherosclerosis and comprised from 67.7 to 87.5 % of the microbial community taxons. 75 % of biopsy samples from atherosclerotic plaques showed growth of the bacteria: Propionibacterium acnes (43.8 %), Staphylococcus epidermidis (18.8 %), Staphylococcus capitis (6.3 %), Staphylococcus saccharolyticus (6.3 %). The common taxons for blood microbiomes and atherosclerotic plaques are Propionibacterium acnes and Bradyrhizobiaceae. 
Discussion. The present study is the first to report the blood microbiome of patients with atherosclerosis and to detect viable cultures of Propionibacterium acnes and Staphylococcus in biopsy samples of atherosclerotic plaques, providing a mechanistic link between microorganisms and cardiovascular disease. Propionibacterium acnes and Bradyrhizobiaceae are common taxons for blood microbiomes and atherosclerotic plaques. It can be assumed that Propionibacterium acnes species is a specific taxon both of atherosclerotic carotid artery plaques and blood of patients with carotid atherosclerosis; additional studies on the etiological significance of the microbial factor in the formation of atherosclerotic plaques are required.

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