A case of brain abscess caused by Propionibacterium acnes 13 months after neurosurgery and confirmed by 16S rRNA gene sequencing.

Propionibacterium acnes is a gram-positive anaerobic bacillus and a normal inhabitant of the skin. Although it is often considered a contaminant of blood cultures, it can occasionally cause serious infections, including postoperative central nervous system infections. Here, we report the case of a 70-yr-old man who developed a large cerebral abscess caused by P. acnes 13 months after neurosurgery. Immediate gram staining of the pus from his brain revealed the presence of gram-positive coccobacilli. However, colony growth was observed only after 5 days of culture. Therefore, we performed 16S rRNA gene sequencing of the pus specimen. The isolate was identified as P. acnes. The colonies developed 9 days after the initial culture. The API Rapid ID 32A test (bioMérieux, France) was performed using a colony, but an unacceptable profile was obtained. Then, the pus was transferred into the enrichment broths of the BACTEC FX (Becton Dickinson, USA) and BacT/Alert 3D (bioMérieux, Organon Teknika, USA) systems, but only the BACTEC FX system could detect growth after 5 days. We performed 16S rRNA gene sequencing and API Rapid 32A profiling with a colony recovered from Brucella agar, which was inoculated with the microbial growth in the enrichment broth from the BACTEC FX system. The organism was identified as P. acnes by both methods. This case suggests that 16S rRNA gene sequencing may be a useful alternative for identifying slowly growing P. acnes from specimens that do not show growth after 5 days of culture.