SAN DIEGO — Mucus plays an important role in helping your body fight off infection, researchers at San Diego State University announced Wednesday.

A team led by Jeremy Barr, a post-doctoral fellow in biology, found that mucus contains bacteria-attacking viruses known as bacteriophage, which shield the body from invading infection.

The scientists said the finding could change the way doctors treat several diseases. The work was published in the May edition of  Proceedings of the National Academy of Sciences.

Protective layers of mucus,  present in all humans and animals, serve both as a home for large populations of beneficial microbes — like fungi, bacteria and viruses — and as an entry point for infection, Barr said.

The researchers sampled mucus from various animals and humans and found that bacteriophage adheres to the mucus layer on all of them by bonding with sugars. E. coli bacteria introduced to the bacteriophage was attacked and killed in their experiments.

By comparison, cells without mucus were three times more likely to die when given bacteriophase and E. coli, the SDSU team reported.

“Taking previous research into consideration, we are able to propose (that) Bacteriophage Adherence to Mucus — or BAM — is a new model of immunity, which emphasizes the important role bacteriophage play in protecting the body from invading pathogens,” Barr said.

Barr said the body invites bacteriophage from the surrounding environment and it sticks to mucus, especially in the mouth and abdominal area. The bacteriophage then becomes a protector of its host, accumulating and attacking on its own, he said.

“This discovery not only proposes a new immune system but also demonstrates the first symbiotic relationship between phage and animals,” Barr said. “It will have a significant impact across numerous fields.”

The SDSU research was funded by the National Institutes of Health.