Understanding changes to the ocular microbial flora can help efforts to develop better diagnostic tools and effective therapies. To that end, researchers have described for the first time the bacterial microbiome of the conjunctiva and cornea of eyes with bacterial keratitis; they found these microbiomes contain increased activity of pathogenic bacteria compared with healthy controls.

Microbiomes are key multispecies communities that colonize various bodily surfaces and vary based on their location. When a microbiome becomes disrupted, often due to disease, it exhibits changes in diversity, abundance and function. This change is known as dysbiosis, and in the case of gut bacteria dysbiosis, it’s been linked to several autoimmune diseases, inflammatory diseases, cancers, mental disorders and ocular diseases.

In this study, the investigators characterized the conjunctival bacterial microbiomes of healthy individuals and those with bacterial keratitis to assess whether ocular microbiome dysbiosis is prevalent among bacterial keratitis patients. They generated microbiomes from conjunctival swabs of healthy controls and from conjunctival swabs and corneal scrapings of bacterial keratitis patients.

There were marked differences between the healthy and bacterial keratitis microbiomes in organism diversity, population and abundance. Elevated levels of Streptococcus, Staphylococcus, Paracoccus, Bosea, Capnocytophaga, Gordonia and Gemella, all pathogens linked with ocular diseases, were found in eyes with bacterial keratitis. The study authors concluded that the increase in pathogenic bacteria in the conjunctiva and cornea in bacterial keratitis may cause or exacerbate ocular surface inflammation. Curiously, abundance of Pseudomonas and Haemophilus, two other common culprits of ocular infection, was lower in this study, underscoring the patient-specific nature of ocular infection pathophysiology.

Shivaji S, Jayasudha R, Chakravarthy SK, et al. Alterations in the conjunctival surface bacterial microbiome in bacterial keratitis patients. Exp Eye Res. 2021;203:108418.