Researchers have identified a protein that powers the virulence of the bacteria that causes gonorrhoea, opening the possibility of a new target for antibiotics and, even better, a vaccine.

Gonorrhoea, a sexually transmitted disease that results in 78 million new cases worldwide each year, is highly damaging if untreated or improperly treated. It can lead to endometritis, pelvic inflammatory disease, ectopic pregnancy, epididymitis, and infertility. Babies born to infected mothers are at increased risk of blindness. The microbe, Neisseria gonorrhoeae, is considered a "superbug" because of its resistance to all classes of antibiotics available for treating infections.

"The infections very often are silent," said a researcher Aleksandra Sikora. "Up to 50 percent of infected women don't have symptoms, but those asymptomatic cases can still lead to some very severe consequences for the patient's reproductive health, miscarriage or premature delivery," he added.

A better antibiotic therapy and a vaccine are needed since N. gonorrhoea strains are resistant to most new treatments. The body relies on enzymes known as lysozymes that, as their name suggests, thwart bacteria by causing their cell wall to lyse, or break apart. Lysozymes are abundant both in epithelial cells, which make up the tissue on the outside of organs and the inside of body cavities and in the phagocytic cells that protect the body by ingesting foreign particles and bacteria.

In turn, many gram-negative bacteria - characterized by their cell envelope that includes a protective outer membrane - have developed ways of defeating lysozymes. Now that new targets have been identified, they can be explored as bullseye candidates for new antibiotics or a vaccine - if the lysozyme inhibitor can itself be inhibited, then the bacteria's infection-causing ability is greatly reduced.

Sikora and her collaborators named the new protein SliC, short for surface-exposed lysozyme inhibitor of c-type lysozyme. Studying SliC's function in culture as well as in a gonorrhoea mouse model - mice were infected with N. gonorrhoea, then checked for SliC expression at one, three and five days - researchers determined the protein was essential to bacterial colonization because of its anti-lysozyme role.

"This is the first time an animal model has been used to demonstrate a lysozyme inhibitor's role in gonorrhoea infection," Sikora said. Sikora also stressed the importance of lysozyme inhibitor. The study appears in PLOS Pathogens journal.