Mucus, along with tears and skin, makes up our first line of defense against disease. They all form a barrier against invading germs. And, as it turns out, according to a study published recently in the "Applied and Environmental Microbiology" journal, the crucial proteins found in mucus known as salivary mucins can protect our teeth from cavity causing bacteria known as Streptococcus mutans. Unlike toothpaste and mouthwash, which destroy bacteria, mucins prevent bacteria from attaching themselves onto your teeth and secreting acid that bores holes through the enamel. Now,the researchers who led the study are trying to engineer synthetic mucus that could be added to toothpaste or bubble gum. Sounds lovely doesn't it?
As disgusting as this sounds, synthetic mucus might go well beyond just preventing cavities. Studies have suggested that mucins might also be able to defend against respiratory infections, stomach ulcers, and even HIV. Since mucins do not actually kill bacteria (they merely prevent bacteria from causing damage), they are seen by some as a much better alternative to antibiotics, which may kill not only harmful bacteria, but helpful bacteria as well, allowing more dangerous strains to take their place. This means that synthetic mucin might offer a less intrusive alternative, used "not necessarily to resolve infections but to stabilize or prevent infections," says Katharina Ribbeck, an assistant professor in the department of biological engineering at MIT, who co-authored this study alongside Erica Shapiro Frenkel, a Ph.D student in her lab.
We get cavities when bacteria such as S. mutans cling to our teeth, forming an intricate, mesh-like arrangement known as biofilm. The bacteria that make up this biofilm feed on the sugars found in the food we eat to produce acid that can then dissolve the tooth enamel. To investigate how much mucus might be needed to guard against this process, Ribbeck's group got down to the molecular level and homed in on a mucin known as MUC5B. This is the most commonly found mucin in the mouth.
First, the researchers isolated MUC5B from saliva samples of some volunteers. Then, they grew S. mutans bacteria with sugar and a special broth in plates containing wells that were made from a plastic which imitates a tooth's enamel. Some of the wells also contained MUC5B. At the end of the experiment, Ribbeck and Frenkel counted the number of attached S. mutans bacteria at several points in time and found more of them floating in the growth broth than attached to the plastic in the wells containing MUC5B. This suggests that the mucin somehow prevents S. mutans from sticking to the surface of the tooth.
How, exactly? The researcher aren't sure, but, according to Ribbeck, it's possible that MUC5B encases S. mutans in a "3-D spiderweb" that traps the acid that they secrete. MUC5B might even form a bacteria-repellent coating over the tooth's surface, or even turn off S. mutans genes that are involved in attachment and biofilm formation. Ribbeck and Frenkel are still trying to find the most likely mechanism, though they suspect that mucins might maintain bacterial diversity in the mouth by not only keeping S. mutans alive, but by also neutralizing the toxins that different bacterial strains release to outdo each other.
Of course, scientists still need to confirm the protective role of mucins before investigating the mechanisms involved. William Bowen, a professor at the University of Rochester's School of Medicine and Dentistry, also points out that cavity-causing bacteria embed themselves in plaque - not directly to the surface of the tooth. And many other bacteria in the mouth cause cavities, not just S. mutans, which is not a "major acid producer."
Still, having said that, Ribbeck and Frenkel have reported similar results with other surfaces, hinting at "a more general mechanism" of MUC5B. Translation? Benefits of synthetic mucus could extend far beyond human health, and could be used to prevent food spoilage, and the accumulation of bacteria on ship hulls and other surfaces, for example. "The applications are enormous," Ribbeck declared.