You may be familiar with the idea that your gut and skin are home to a collection of microbes – fungi, bacteria and viruses – that are vital for keeping you healthy. But did you know that your eyes are also a unique menagerie of microbes?
Together they are called the eye microbiome. When these microbes are out of balance – too many or too few of certain types – eye diseases may emerge
With a recent study showing bacteria live on the surface of the eye and stimulating protective immunity, scientists are beginning to discover the microbial factors that can be exploited to create innovative therapies for a range of eye disorders such as Dry Eye Disease, Sjogren's Syndrome and Corneal Scarring
I ' m an immunologist studying how the eye prevents infection. I became interested in this field because people get only two eyes, and understanding how bacteria affect immunity may be the key to avoiding up to 1
When discussing the microbiome, most scientists usually think of the gut, and deservedly so; researchers think one colon can harbor more than 10 trillion bacteria. That is being said, more attention is now focused on the impact microbiomes have on other sites, including the skin, and areas with very few bacteria, such as the lungs, vagina and eyes
For the last decade, microbiome in ocular health was controversial. Scientists believe that healthy eyes lacked an organized microbiome. Studies show that bacteria from the air, hands or eyelid margins could be present on the eye; however, many believed these microbes were simply killed or washed away by the continuous flow of tears
Only the recent scientists have concluded that the eye does indeed have a "core" microbiome that appears to be dependent on age, geography, ethnicity, contact lens wear, and state of disease. four genera of bacteria Staphylococci Diphtheroids Propionibacteria and Streptococci . In addition to these bacteria, the torque teno virus, implicated in some intraocular diseases, also counts as a member of the core microbiome as it is present on the surface of the eye by 65% of healthy individuals.
This suggests that doctors should think more deeply about the risks and benefits to the microbiome when prescribing antibiotics.
In a recent study spanning more than a decade and including more than 340,000 patients in the US, the authors found that antibiotics were used to treat 60 percent of acute conjunctivitis (pink eye) cases
But viral infections are the most likely causes of pink eye and not treatable with antibiotics. More striking, even cases caused by bacteria often resolve in 7-10 days without intervention. It is well known that excessive or inappropriate antibiotic use can disrupt the microbiome, leading to infection, autoimmunity and even cancer
Discovering an eye-colonizing microbe
Within the past decade, studies evaluating the eye microbiome and disease have boomed. They have generated an immense amount of data, but most of it is correlative.
This means that certain bacteria have been linked to certain diseases, such as Sjogren's Syndrome or bacterial keratitis.
During my time at the National Eye Institute, I used a mouse to identify whether bacteria at the surface of the eye could stimulate an immune response to protect the eye from blinding pathogens like the bacterium Pseudomonas aeuruginosa In 2016, the ocular immunologist Rachel Caspi at the National Eye Institute and I hypothesized that the protective bacteria were living near or on the eye. Indeed, we found a resident bacterium, Corynebacterium mastitidis ( C. mast ), which stimulates immune cells to produce and release antimicrobial factors that kill harmful microbes in the tears. and a series of experiments, the Caspi lab was able to show for the first time a causal relationship between C. ointment and a protective immune response. Whenever C. Candida albicans and Pseudomonas aeuruginosa .
Now, in my lab, we would like to exploit this relationship between C. osteoarthritis and ocular immunity to develop novel therapies to prevent infection and possibly target more widespread diseases like Dry Eye Disease
Engineering microbes to improve eye health
The first step toward developing such therapies is figuring out how bacteria colonize the eye. For this, my lab collaborates with the Campbell Laboratory at the University of Pittsburgh, which houses one of the most extensive collections of human ocular bacteria in the country.
With our unique experimental setup with mice and advanced genetic analyzes, we can Use this microbial library to identify the specific factors required for the microbes to colonize the surface of the eye
Then, with ophthalmologists and optometrists in the UPMC Eye Center, we are beginning to analyze the immune signatures within the eyes of healthy and diseased patients
Here, our hope is to use this technology as a new diagnostic tool to target the microbes causing disease rather than immediately treat infections with broad spectrum antibiotics that kill the good microbes too
Finally, one of our loftier goals are to genetically engineer eye-colonizing bacteria to act as long-term delivery vehicles to the surface of the eye. In the gut, genetically modified bacteria have been shown to alleviate diseases like colitis
We hope that this new "prob-eye" treatment would act to secrete immune regulatory factors, which would limit the symptoms associated with conditions such as Dry Eye Disease, which affects about 4 million people in the US per year
In this developing field, there is still much to learn before physicians can begin manipulating the ocular microbiome to fight disease. But one day, perhaps rather than just squirting your eye drops into your dry eyes, you will squirt in a solution with some bacteria that will colonize your eye and secrete the lubricants and other factors your body is missing. Stay tuned.
Leger, Assistant Professor of Ophthalmology and Immunology, University of Pittsburgh
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