Scientists Discover New Properties of Microbes That Cause Common Eye Infection

Scientists from Massachusetts Eye and Ear/Harvard Medical School Department of Ophthalmology have used the power of new genomic technology to discover that microbes that commonly infect the eye have special, previously unknown properties. These properties are predicted to allow the bacterium -- Streptococcus pneumoniae -- to specifically stick to the surface of the eye, grow, and cause damage and inflammation.

Researchers are now using this information to develop new ways to treat and prevent this bacterium, which is becoming increasingly resistant to antibiotics. Their findings are in the current issue of Nature Communications.

S. pneumoniae is a leading cause of infection and is responsible for diseases ranging from infection of the lungs, pneumonia, to infection of the brain, to infection of the surface of the eye known as conjunctivitis. Although infection of the eye can usually be safely treated, S. pneumoniae infection is a leading cause of illness and death worldwide.

According to Massachusetts Eye and Ear researcher Michael S. Gilmore, the Sir William Osler Professor of Ophthalmology at Harvard Medical School, an effective vaccine is available that helps prevent many of the most severe types of infection. "I believe it is especially important for children and the elderly to be vaccinated. The vaccine causes the body to react to a slimy coating on the bacterial surface called a "capsule." The capsule allows S. pneumoniae to escape from white blood cells that try to eliminate it, and S. pneumoniae goes on to cause lung and other infections."

However, the strains of S. pneumoniae that cause eye infection have been known to lack this capsule, yet they still cause infection. "Because they lack the capsule, they are not affected by the vaccine either," he says.

To design a better vaccine, and to understand how these "unencapsulated" strains of S. pneumoniae are still able to cause infection of the ocular surface, the research team, spearheaded by postdoctoral researcher Michael Valentino and including Mass. Eye and Ear scientists Wolfgang Haas and Paulo Bispo, as well as a collaborative team from the Broad Institute of Harvard University and Massachusetts Institute of Technology, the Centers for Disease Control and Prevention, and elsewhere, examined the genomes of a large collection of S. pneumoniae strains collected from across the United States.

"We found that about 90 percent of the conjunctivitis strains were very closely related and formed a new group of S. pneumoniae with infectious properties that were different from any other known strains," Gilmore says. "These new properties are believed to allow S. pneumoniae to resist the normal clearance mechanisms of the surface of the eye, including blinking and tears, stick to the eye surface, grow there and cause damage."

Gilmore believes that including some of the S. pneumoniae proteins that allow the bacterium to do this in a new type of vaccine, might lead to the prevention of nearly 90 percent of the cases of conjunctivitis caused by this microbe and save the use of antibiotics for more severe infections.

The paper, "Unencapsulated Streptococcus pneumoniae from conjunctivitis encode variant traits and belong to a distinct phylogenetic cluster," appears in the Nov. 13 issue of issue of the prestigious international science journal, Nature Communications.

Portions of this project were supported by NIH grants EY024285, Molecular Basis for Ocular Surface Tropism in Conjunctivitis and by the Harvard-wide Program on Antibiotic Resistance, AI083214. Additional support for this project was obtained from the ALSAC organization of St Jude Children's Research Hospital. In addition, portions of this project were supported by Bausch and Lomb Inc.

Source: Massachusetts Eye and Ear