By NORBERT HERZOG and DAVID NIESEL
Though it has a reputation as slimy and gross, mucus is one of the most valuable lines of defense against the bacteria people are exposed to every day. It exists not only in a person’s nose, but the respiratory, digestive, urogenital, visual and auditory systems.
Science now shows it contains viruses called bacteriophage (phage for short) that attack and kill bacteria.
A virus is a tiny, infectious agent that is made of a protein coating and a core of genetic information. Although viruses can carry genetic information, undergo mutations and reproduce, they cannot metabolize on their own and thus are not considered alive.
Viruses are classified by the type of genetic information they contain and the shape of their protein capsule. There are viruses that infect every living thing on earth. There are even viruses that infect other viruses. Certain viruses that can infect bacteria have been found in mucus.
A healthy adult produces about 1 to 11⁄2 liters of mucus per day. Mucus consists of water, salts, antibodies, enzymes and a family of proteins called mucins. Different mucins are responsible for signaling between cells, forming a chemical barrier for protection and working with the immune system.
Scientists know that wherever bacteria live, there are also phage viruses that infect them. Areas with mucus have 40 phage for every bacterium, while that ratio is only 5 to 1 in areas without mucus. To discover what these phage are doing in the mucus, scientists grew two types of lung tissue in the lab — one that produces mucus and one that cannot.
When both lung cultures were exposed to the bacteria E. coli, about half the lung cells died. However, when phage that kill the bacteria were added, the lung cells in the presence of mucus survived. This suggests that the combination of phage and mucus can efficiently kill potentially harmful bacteria.
The researchers also discovered that the outside of phage is studded with antibody-like proteins that attach the phage to the carbohydrates in the mucus. This would help keep the phage where the bacteria are likely to be. The host may use this system to select which phage are localized to the mucus layers and which can be washed away, explaining why beneficial bacteria are not harmed by phage.
An important implication of this system is that it controls the microbial populations in the digestive tract, which play a role in obesity, diabetes and inflammatory bowel disease.
It all started with investigating how phage actually work in the body. Scientists uncovered the revelation that there are in fact beneficial viruses. In the future, this research could be the foundation for designing phage that reside in mucus and combat specific bacteria or even change the body’s microbiome.
Professors Norbert Herzog and David Niesel are biomedical scientists at the University of Texas Medical Branch. Learn more at medicaldiscoverynews.c