The Ocular Microbiome

About five years ago, Valery Shestopalov of the Bascom Palmer Eye Institute at the University of Miami was speaking with his microbiology colleagues about the bacteria found on healthy eyes. Conventional wisdom at that time held that healthy eyes don’t harbor much microbial life—tears and blinking tend to clear away foreign objects, including bacteria. But Shestopalov’s early tests revealed something different. “The tests ran positive. All exposed mucosal epithelium are populated densely,” he said. In 2009, Shestopalov began the Ocular Microbiome Project with funds from his institution. Eventually, he secured a grant from the National Eye Institute and began collaborating with Russell Van Gelder at the University of Washington, who had been developing PCR-based diagnostic tests to identify bacteria and fungi on the eye. The project now has a dozen collaborators at five universities.

The team found that about a dozen bacterial genera dominated the eye’s conjunctiva, a third of which could not be classified. On the corneal surface, the researchers found a slightly different community. Again, about a dozen genera dominated. And everywhere they’ve looked, the researchers have found more than just bacteria.

The researchers also found that during keratitis infections—infections of the cornea—only about half as many bacterial varieties were present, most prominently Pseudomonas strains. The changes typically occurred well before a diagnosis of an eye infection, suggesting the ocular microbiome could inform future diagnostic.

One factor that may be expected to impact the composition of ocular microbiota is the use of contact lenses. Contact lens wear is one of the biggest factors leading to corneal infection. Common bacterial infections that can cause irritation and redness affect an estimated 7 percent to 25 percent of contact lens–wearers, and much rarer keratitis infections can even cause blindness. Researchers believe contact lenses make it easier for pathogens to colonize the surface of the eye by giving the bacteria something to adhere to. Sequencing biofilms from used contact lenses, Shestopalov’s team found evidence of microbial communities that were different from the ocular microbiomes of people who don’t use contacts.

A version of this article appeared on www.the-scientist.com.
Posted by Tim Sandle