Multiple bacteria in aortic aneurysms

Objective: The purpose of the present study was to reexamine the possibility that bacteria, particularly anaerobes, are present in aortic aneurysms. Methods: From December 2000 to November 2001, 53 samples from aneurysm walls were collected from 49 patients during reconstructive surgery. The tissue specimens were sectioned and cultured under anaerobic conditions. Twenty-eight specimens were also subjected to scanning or transmission electron microscopy. Results: Anaerobic cultivation yielded bacteria in 14 of the 53 samples (26.4%). All bacteria were gram-positive cocci or rods from nine genera and 12 species. Five cultures (35%) were mixed, containing two bacterial species. Mixed aerobic and anaerobic species were found in four samples (28.5%). Anaerobic bacteria were recovered from 10 of 14 positive cultures (71%). Among anaerobes found were Propionibacterium acnes, Propionibacterium granulosum, Actinomyces viscosus, Actinomyccs naeslundii, and Eggerthella lenta. Coaggregating bacteria of different sizes and structure were found on the aneurysm walls and inside the intravascular plaque at electron microscopy. Bacteria were found in 20 of the 28 samples (71%) examined with scanning or transmission electron microscopy. Conclusion: Multiple bacteria, many of which did not belong to the indigenous skin microflora, colonize aortic aneurysms. It is not clear whether the bacteria contribute to weakening of the aortic wall by eliciting inflammation or whether they are secondary colonizers of aneurysms.