The bacterium Propionibacterium acnes may cause ocular sarcoidosis, as researchers have detected high levels of the pathogen in retinal granulomas of patients with the condition. These findings suggest that new therapies for the disease may include antibiotics targeting the infection.
The study, “Immunohistochemical Detection of Propionibacterium acnes in the Retinal Granulomas in Patients with Ocular Sarcoidosis,” was published in the journal Scientific Reports.
While the causes of sarcoidosis are still not fully known, two bacteria — mycobacteria and Propionibacterium acnes — are established factors underlying the disease in the United States and Europe (mycobacteria) and Japan (Propionibacterium acnes).
While Propionibacterium acnes is suggested to cause systemic sarcoidosis, it’s presence in the retina — the light-sensitive tissue lining the back of the eye — and, consequently, its contribution to ocular sarcoidosis are less studied.
The study’s authors analyzed biopsied retinas from patients with ocular sarcoidosis to see if they could detect the presence of Propionibacterium acnes.
The team recruited 11 patients (12 eyes) with sarcoid uveitis, an inflammation of the eye’s uvea, and as controls, the study enrolled eight individuals with displaced retina (called rhegmatogenous retinal detachment), two with non-sarcoid uveitis, and two with vitreoretinal lymphoma.
Results showed that while a high proportion of patients with ocular sarcoidosis (82%) showed signs of the presence of Propionibacterium acnes, control subjects were bacterium-free and authors detected zero cases of Propionibacterium acnes.
Curiously, the team noted that the detection rate of Propionibacterium acnes in the retina exceeded that of lung samples — 82% versus 74%, respectively — which by comparison are significantly much larger than the retina. They hypothesized that the degradation rate in the retina, which is much lower than that of the lungs, may explain this observation.
“Given that the retina is an aseptic environment, the presence of P. acnes within the retina is extremely unusual. In fact, no P. acnes were detected within retinas in the control group in the current study. Therefore, detecting P. acnes within retinas is a critical finding for confirming the role of P. acnes as an etiological agent of sarcoidosis,” researchers wrote.
Overall, identifying Propionibacterium acnes as a causal factor “may facilitate the development of novel treatments for ocular sarcoidosis, i.e., a combination of curative treatment, such as antibiotics to reduce P. acnes, and symptomatic therapy,” the team concluded.