Clinical characteristics of lung abscess by red complex bacteria infection: a case report and literature review.

BACKGROUND: Treponema denticola, Porphyromonas gingivalis and Tannerella forsythia are common oral pathogens collectively referred to as the "red complex bacteria", serve as crucial periodontopathic agents. Owing to the challenges associated with anaerobic culture, their contribution to lower respiratory tract infections, especially lung abscess, is often undervalued. Metagenomic next-generation sequencing (mNGS) has evolved as a potent instrument for the identification of fastidious organisms.

CASE PRESENTATION: A 63-year-old male with chronic cough and hemoptysis was admitted to our hospital. Chest computed tomography showed an indeterminate space-occupying lesion in the right upper lobe, and repeated sputum cultures were negative. Lung cancer was the primary consideration, so a CT-guided percutaneous core needle biopsy of the lung lesion was performed. Nevertheless, the pathology favored inflammation over lung cancer, leading us to continue investigating the causative pathogen. Following mNGS analysis of the puncture biopsy tissue, Treponema denticola and Porphyromonas gingivalis were detected. Both organisms belong to the red complex bacteria, closely associated with periodontitis that the patient had. Intravenous piperacillin-tazobactam followed by oral amoxicillin-clavulanate was prescribed. The patient recovered and subsequent chest computed tomography confirmed the improvement.

CONCLUSIONS: This case highlights the role of oral red complex bacteria in culture-negative chronic lung abscesses. mNGS is a crucial diagnostic tool for identifying these fastidious anaerobes, enabling targeted therapy and improving clinical outcomes.