BACKGROUND: Pseudopropionibacterium propionicum was called Propionibacterium propionicum until a recent taxonomy change in 2016. Diseases caused by P. propionicum resemble actinomycosis and thus differ dramatically from the infectious syndromes caused by common cutaneous Propionibacterium spp. However, if treating physicians are not familiar with P. propionicum and its clinical presentations, it is possible for them to regard it as a skin contaminant such as Cutibacterium acnes (formerly Propionibacterium acnes).

CASE REPORT: A 71-year-old man with past surgical history of right pneumonectomy was admitted with right chest wall abscess and right empyema. The chest wall abscess was drained surgically, and the empyema was drained via a chest tube. The abscess culture took 5 days to grow beaded branching Gram-positive rods, and 15 days to identify them as P. propionicum. The patient received 17 days of ceftriaxone and 4 weeks of doxycycline. However, he experienced a relapse of the chest wall abscess and right empyema 4 months after discontinuation of doxycycline. Cultures from the chest wall abscess and empyema grew P. propionicum again. We treated him with ceftriaxone for 6 months followed by minocycline for 7 months along with adequate drainage.

CONCLUSIONS: It is important to recognize that P. propionicum can cause thoracic actinomycosis and will likely require the prolonged treatment course typical for actinomycotic disease, which is 2 to 8 weeks of intravenous antibiotic therapy followed by 6 to 12 months of oral antibiotic therapy.

Keywords: Actinomycosis, Classification, Empyema, Pleural, Propionibacterium, Abscess, Propionibacteriaceae, Thoracic Diseases, Thoracic Wall