This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Aerial disorders, Subject name: Surgery
[{'content': 'What is the most common organism that causes infected abdominal aoic aneurysms (AAAs)? \nSelect and explain. \nA. Escherichia coli, B. Bacteroides, C. Salmonella, D. Pseudomonas aeruginosa', 'role': 'user'}, {'content': 'Answer: C \nExplanation: 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.', 'role': 'assistant'}]