Abstract

Introduction: Inflammation is a hallmark of aneurysmal disease, but the etiology for the inflammation is unknown. Previously, bacteria and bacterial nucleic acid sequences have been identified within abdominal aortic aneurysm tissue. However, only one study has taken an un-targeted approach to assess the diversity of species and no study has surveyed bacterial species across the various environments in patients with aortic disease. Research Question: Does the distribution of bacterial sequences differ between environments and by disease status in patients with abdominal aortic disease? Methods: Whole blood, acute (luminal) thrombus, chronic (medial/abluminal) thrombus, and aortic wall specimens were obtained from 14 patients undergoing open aortic surgery. Five patients had aneurysm disease and nine patients had aortic occlusive disease. Sequencing using universal primers targeting the V3 - V5 16s rRNA bacterial gene was performed. Reads were processed and aligned to reference banks using QIIME2 to the genus level. Results: The average patient age was 60.9 years with no significant difference in baseline demographics. Phyllobacterium was the most common genus identified in acute and chronic thrombus for aneurysmal and occlusive disease while pseudomonas was the most common genus identified in aortic wall. Chao1 alpha diversity was higher in aneurysmal aortic wall samples compared to occlusive disease (10.6 vs 6.6, p=0.047). On principle component analysis, samples from similar tissue environments cluster together with 16% of the sequence variation explained by the grouping (p=0.003, Figure 1). Conclusions: The diversity of bacterial sequences groups by microenvironment within patients with aortic disease, suggesting a spectrum of bacterial communities that progress from blood through the luminal thrombus to the aortic wall. Further work could distinguish genus level variations that associates with disease in the different environments.