A Case of Psoas Abscess Diagnosed With Oral Bacteria as the Causative Pathogen

We report a rare case of a psoas abscess in an 87-year-old woman, in which oral commensal bacteria may have disseminated hematogenously from a chronic oral infection site and served as the causative pathogens. The patient presented with persistent left buttock pain, fever, and swelling, and imaging revealed a fracture of the left iliac bone with an associated psoas abscess. Bacterial cultures identified <i>Streptococcus oralis</i> and <i>Pseudomonas aeruginosa</i>. Her symptoms improved following antibiotic therapy and CT-guided drainage. Although the presence of <i>P. aeruginosa</i> in the oral cavity is generally considered transient, it has been isolated from the oral cavities of elderly and immunocompromised individuals. In the absence of lacerations or other direct portals of entry, and considering the identification of both pathogens, the oral cavity was regarded as the most likely source of infection. This case highlights the importance of correlating culture results with the most probable source of infection to improve the prognosis of systemic infections.