Mycotic Abdominal Aortic Aneurysm Caused by Bacteroides Thetaiotaomicron and Acinetobacter Lwoffii: The First Case in Korea
A 60-year-old man was admitted to a hospital because of a 10-day history of lower abdominal pain and fever. His past medical history included diabetes mellitus, which was poorly controlled (HbA1c level of 11.2%). He had no history of recent infection, acupuncture, or intravenous injection.\nOn admission, he was febrile and complained of lower abdominal pain, but no abdominal tenderness or rebound tenderness was elicited. Other meaningful symptoms and signs suggesting metastatic complications (endophthalmitis, central nervous system infection, etc.) were not present. His initial vital signs included high fever (39.0℃), blood pressure of 140/80 mmHg, a heart rate of 92 beats/min, and a respiration rate of 20 breaths/min.\nLaboratory investigations showed a white blood cell (WBC) count of 8,610/mm3 (neutrophils, 83.9%; lymphocytes, 7.3%; monocytes, 6.3%; basophils 0.3%), a hemoglobin level of 13.6 g/dL, and a platelet count of 122,000/mm3. The C-reactive protein (CRP) level was 16.56 mg/dL.\nEnhanced computed tomography (CT) revealed a mycotic aneurysm originating from the abdominal aorta (), and no other infectious focus was observed on abdominal CT. A transthoracic echocardiogram did not reveal any evidence of infective endocarditis.\nThe patient was diagnosed with an abdominal aortic mycotic aneurysm. Because the patient had poorly controlled diabetes mellitus and mycotic aneurysm has a high mortality rate and can be caused by various organisms, strong broad-spectrum intravenous antibiotic therapy was immediately initiated (intravenous 1g q8hr of meropenem plus 200 mg q24hr of teicoplanin). The fever was controlled and the CRP level decreased during eight days of antibiotic therapy. However, even with intravenous antibiotics, he continued to complain of abdominal pain.\nThe patient's vital signs were stable without fever and laboratory-tested parameters did not worsen. However, we conducted a follow-up enhanced CT to assess the need for surgical management (8 hospital days). Enhanced CT showed an enlarged aneurysm in a state of impending rupture (). Surgery was immediately performed to address the infection. Massive atherosclerotic changes and plaque formation were observed in the intima of the abdominal aorta, and inflammatory change was noted from 1 cm below the renal artery bifurcation to the iliac artery bifurcation. The infected aortic wall was debrided and an aorto-bi-external iliac artery bypass was performed.\nLater, two out of three anaerobic blood cultures were positive for unidentified bacilli. To identify the isolate, 16S rRNA was sequenced (Macrogen, Daejeon, Korea). In brief, DNA was extracted and PCR was performed using primers targeting the 16S rRNA region, followed by purification, the sequencing reaction, and analysis. The resulting sequence was compared with sequences stored in the GenBank () and EzTaxon () databases, and one isolate was identified as B. thetaiotaomicron, with a percentage identity of 98.08%. Tissue biopsied from the wall of the aortic aneurysm was also positive for A. lwoffii, which was detected using standard microbiological methods. The following minimum inhibitory concentrations (MIC via VITEK II) were recorded: ampicillin/sulbactam 2; amikacin 2; ciprofloxacin 0.25; colistin 0.5; cefepime 1; imipenem 0.25; meropenem 0.25; ceftazidime 1; cefotaxime 8; and piperacillin/tazobactam 4. According to the microbiological results, the antibiotic therapy was changed from meropenem plus teicoplanin to ciprofloxacin plus metronidazole (intravenous 500 mg q12hr of ciprofloxacin and 500 mg q8hr of metronidazole).\nThe day after surgery, the patient had no fever and laboratory data indicated an improvement. Enhanced CT performed on day 7 after surgery () revealed no serious complications or re-infection. After 12 days of intravenous antibiotic therapy, the WBC count and CRP level had decreased to within the normal range. The patient recovered and was discharged. He remained in good condition and continued to take oral ciprofloxacin and metronidazole for 13 days after surgery. He is being followed-up at the outpatient clinic and is reported to be in good condition.