What is the most common organism that causes infected abdominal aoic aneurysms (AAAs)?

There are four different causes of an infected aneurysm. (1) Mycotic aneurysms involve a septic embolus from the hea infecting an aery. (2) Microbial aeritis involves bacteria infecting an athero- sclerotic aery to cause aneurysmal degeneration (80% of infected aneurysms). (4) Traumatic pseudoaneurysm that has concomitant bacterial inoculation. Salmonella causes 40% of all aneurysmal infections, with most others being caused by Streptococcus, Staphylococcus, Bacteroides, E. coli, and P. aeruginosa. Blood cultures are positive in only 50% of cases.