A rare brain abscess caused by co-infection with Fusobacterium nucleatum and Actinomyces meyeri : Case report and a literature review.

Brain abscesses are rare but life-threatening infections that may result from contiguous spread or hematogenous dissemination, with odontogenic infections being an important source. We report the first case from Turkey of a polymicrobial brain abscess caused by Actinomyces meyeri and Fusobacterium nucleatum in an immunocompetent 81-year-old male with poor oral hygiene and a history of untreated dental infection. The patient presented with headache and altered mental status, and neuroimaging revealed a right frontal abscess. Surgical excision was performed, and microbiological evaluation identified both pathogens by anaerobic culture and matrix-assisted laser desorption/ionization time-of-flight (MALDI-TOF) mass spectrometry, with susceptibility testing confirming sensitivity to β‑lactams and metronidazole. Notably, follow-up oral swab culture yielded A. meyeri with an identical susceptibility profile, supporting a dental origin of infection. The patient was successfully treated with surgical drainage and high-dose penicillin G combined with metronidazole followed by oral therapy, with no recurrence observed at 3 months. This case emphasizes the role of odontogenic infections as a source of intracranial abscesses and highlights the importance of microbiological and molecular methods for accurate pathogen identification and therapeutic guidance.