Identification of the causative organisms in 17 cases of infected abdominal aortic aneurysms using ribosomal RNA gene sequencing analysis and genetic study on 10 cases of Helicobacter cinaedi.

Infected abdominal aortic aneurysm (IAAA) is a life-threatening condition, often complicated by a high rate of culture-negative cases, which hampers appropriate antimicrobial selection. This study investigated the causative organisms in 17 patients who underwent surgery for IAAA at two institutions in Japan. Pathogens were identified through blood and tissue cultures, ribosomal RNA gene sequencing, and histopathological examination. In cases where Helicobacter cinaedi was detected, multilocus sequence typing (MLST) and genetic analyses for resistance to β-lactams, macrolides, and quinolones were conducted. Of the 17 cases, 11 (64.7%) were culture-negative, and H. cinaedi was identified in 8 (72.7%) of these through rRNA gene analysis. Including 2 culture-positive cases, H. cinaedi was found in 10 cases (58.8%) overall. All H. cinaedi cases harbored genetic mutations associated with macrolide resistance and amino acid substitutions linked to quinolone resistance, while no mutations related to β-lactam resistance were detected. These findings indicate that H. cinaedi is a predominant pathogen in culture-negative IAAA and suggest that β-lactam antibiotics are appropriate for treatment, whereas macrolides and quinolones should be avoided.