Corynebacterium acnes can be identified if grown anaerobically on brain heart infusion agar with 1% polysorbate 80 (Tween 80) added. One millimeter dome-shaped, grayish-white colonies appear in three to five days. Smears reveal thin, gram-positive rods, singly or in pairs, and stain unevenly. A catalase test is positive. These colonies, subcultured on blood (sheep) agar, do not grow aerobically but flourish anaerobically as a profusion of pinpoint, translucent colonies at 37 C. Positive agglutinations are produced by C acnes antisera No. 554 or 605, or both. Gas chromatographic analysis of the bacterial fatty acids demonstrates a predominance of iso-C15 branched fatty acid.
Ray LF, Kellum RE. Corynebacterium acnes From Human SkinIdentification by Morphologic, Cultural, Biochemical, Serological, and Chromatographic Methods. Arch Dermatol. 1970;101(1):36-40. doi:10.1001/archderm.1970.04000010038005