Thoracic empyema caused by Alloscardovia omnicolens and Bifidobacterium dentium

A 62-year-old man was admitted to our emergency department with the complaint of worsening dyspnea after initiating anti-tuberculous therapy (isoniazid [300 mg/day], rifampicin [600 mg/day], ethambutol [750 mg/day], and pyrazinamide [1,500 mg/day]) for tuberculous pleuritis. His oral hygiene status was poor. The patient had no significant past medical history. However, he had a history of smoking (10 cigarettes per day for 45 years) and was a social drinker. Chest radiography revealed increased right pleural effusion and pneumothorax. The pleural fluid was purulent, and the culture grew Alloscardovia omnicolens, Bifidobacterium dentium, and Prevotella loescheii. He was treated with antibiotics (3 g of intravenous ampicillin/sulbactam every 6 h, which was changed to oral amoxicillin/clavulanate potassium on day 34) in addition to anti-tuberculous therapy, he underwent chest tube insertion, and subsequently improved. Bifidobacteriaceae are commensal flora of the mouth and pulmonary infections caused by these organisms are extremely rare. Nevertheless, clinicians should consider these organisms as a possible cause of pulmonary infections, and consider that respiratory infections caused by commensal flora of the mouth may occur during the treatment of other diseases in patients with poor oral hygiene.