Bacterial diversity in aortic aneurysms determined by 16S ribosomal RNA gene analysis.

Background: Aortic aneurysms are common vascular conditions that cause considerable morbidity and mortality. Understanding of the mechanisms involved in the pathogenesis of the condition remains limited. Recently, infection has been suggested as possible contributor in the development of the disease. The aim of the present study was to examine aortic aneurysms for the presence of bacterial DNA using polymerase chain reaction (PCR) targeting the 16S ribosomal RNA (rRNA) gene, followed by cloning and sequencing.

Methods: Universal eubacterial primers were used to amplify 16S rRNA bacterial genes in 10 specimens from arterial walls of aortic aneurysms. Subsequently, PCR amplicons were cloned into Escherichia coli and sequencing of the cloned inserts was used to determine species identity or closest relatives by comparison with known sequences in GenBank.

Results: Sequences of Stenotrophomonas spp., including S. maltophilia (formerly Pseudomonas homology group V) were detected in six aneurysm samples. Propionibacterium acnes was identified in five samples, and Brevundimonas diminuta (formerly P. diminuta) in four samples. Other species previously assigned to the Pseudomonas genus such as Comamonas testosteroni, Delftia acidovorans, Burkholderia cepacia, Herbaspirillum sp., and Acidovorax sp. were also detected. Some clones fell into other environmental species, including Methylobacterium sp. and Bradyrhizobium elkanii, and others represented bacteria that have not yet been cultivated. DNA sequences from oral bacteria, including Streptococcus sanguinis, Tannerella forsythia, and Leptotrichia buccalis were detected. Sequences from Prevotella melaninogenica and Lactobacillus delbrueckii, which are commonly found in both mouth and gastrointestinal tract, were also detected. Additional species included Dermacoccus spp. and Corynebacterium vitaeruminis.

Conclusions: A wide variety of bacteria, including oral bacteria, was found to colonize aortic aneurysms and may play a role in their development. Several of these microorganisms have not yet been cultivated.

Clinical Relevance: Although Chlamydophila pneumoniae has been detected in aneurysmal walls, its exact role in the condition remains inconclusive. Overall, there is scarce information about the role of microorganisms in aneurysmal disease. In the present study, we used molecular genetics to detect a diversity of bacteria in arterial walls of aortic aneurysms. The presence of multiple microorganisms in aneurysmal disease may have implications for chemoprophylaxis and antibiotic treatment if directed only at C.pneumoniae.