Pulmonary actinomycosis caused by Actinomyces cardiffensis.

We herein present the first case of pulmonary actinomycosis caused by Actinomyces cardiffensis (A. cardiffensis). A computed tomography (CT) examination revealed a nodule with cavitation in the left upper lobe of the lung. One month later, the lesion had almost disappeared, but a new nodule with peripheral consolidation had appeared in the right middle lobe. Because organizing pneumonia was suspected, prednisolone was begun and improvement was seen. However, two months after the initiation of corticosteroid administration, a chest CT scan showed a lung abscess. The patient underwent surgical resection of the abscess. A. cardiffensis was identified by an amplified 16S ribosomal DNA restriction analysis of a pus sample.