Dual Role of Cutibacterium acnes: Commensal Bacterium and Pathogen in Ocular Diseases

Microbiota present around the ocular surface, encompassing the eyelid skin, the conjunctival sac, and the meibomian glands, play a significant role in various inflammatory conditions associated with the ocular surface. <i>Cutibacterium acnes</i> (<i>C. acnes</i>), formerly, <i>Propionibacterium acnes</i>, is one of the most predominant commensal bacteria and its relative abundance declines with aging. However, it can act as both an infectious and an immunogenic pathogen. As an infectious pathogen, <i>C. acnes</i> has been reported to cause late onset endophthalmitis post-cataract surgery and infectious keratitis. On the other hand, it can trigger immune responses resulting in conditions such as phlyctenules in the cornea, chalazion in the meibomian glands, and granuloma formation in ocular sarcoidosis. This review explores the role of <i>C. acnes</i> in ocular inflammation, specifically highlighting its implications for diagnosis and management.