Pulmonary Abscess Caused by Cutibacterium acnes in an Immunocompetent Patient: A Case Report and Review of the Literature

Cutibacterium acnes (formerly Propionibacterium acnes) is a gram-positive, strict anaerobic bacillus that is part of the normal skin and mucosal microbiota. It is recognized as an opportunistic pathogen, mainly involved in implant-associated infections. Pleuropulmonary localizations remain exceptional, and parenchymal involvement is rare, most often in immunocompromised patients or those with severe underlying respiratory diseases. We report the case of a 34-year-old chronic smoker, immunocompetent, who presented with a one-year history of productive cough, progressive dyspnea, hemoptysis, fever, and weight loss. Chest imaging revealed a cavitary consolidation in the right upper lobe associated with mediastinal lymphadenopathy, initially suggestive of pulmonary tuberculosis or lung malignancy. Laboratory findings showed an inflammatory syndrome (white blood cell count 12,000/mm³; C-reactive protein 132 mg/L). Repeated microbiological investigations as well as bronchial and CT-guided transthoracic biopsies were negative, showing neither malignancy nor granulomatous inflammation. Due to clinical and radiological worsening, a surgical biopsy via thoracotomy was performed. Bacteriological analysis yielded a positive culture for C. acnes, leading to the diagnosis of lung abscess caused by this organism. The patient received ceftriaxone 2 g/day for six weeks, with favorable clinical, biological, and radiological outcomes, including resolution of hemoptysis, improvement of respiratory symptoms, normalization of inflammatory markers, and significant radiological regression. Pleuropulmonary infections of C. acnes are rare and typically characterized by an insidious clinical presentation related to the organism’s slow growth. Diagnosis is challenging because of the risk of sample contamination and the need for prolonged and appropriate anaerobic culture conditions. This case highlights that C. acnes may cause lung abscess even in immunocompetent patients and may mimic more common conditions such as tuberculosis or lung cancer. Early recognition and appropriate antibiotic therapy are essential to ensure favorable outcomes.