Why you should care

Because cleaning our teeth with mucus could be the future of dental hygiene.

You brush. You floss daily (OK, weekly… or is it monthly?). Twice a year, you grit your teeth and do your best to take whatever your dentist dishes out with her scraping, buzzing, incomprehensible tools of oral torture. So we’re sad to break the following news: The best defense against cavities might not be your own diligence, much less those fluoride treatments, sealants or fillings. In fact, the silver bullet feels warm, moist and even a bit slimy. That’s right: snot.

Mucus, along with skin and tears, makes up our first line of defense against disease. They form a physical barrier against invading germs. And, as it turns out, crucial proteins in mucus called salivary mucins protect our teeth from a type of bacteria that’s responsible for causing cavities, known as Streptococcus mutans, according to a study published this year in the journal Applied and Environmental Microbiology. Unlike toothpaste and mouthwash, which kill bacteria, mucins prevent bacteria from latching onto teeth and secreting acid that bores holes through a tooth’s hard outer surface, or enamel. Now, researchers who led the study are engineering synthetic mucus that could be added to toothpaste or chewing gum. Booger bubble gum, anyone?

As gross as it sounds, synthetic mucus might go well beyond preventing cavities. Studies suggest that mucins might also defend against respiratory infection, stomach ulcers and even HIV, for example. Since mucins don’t kill bacteria (they merely prevent bacteria from inflicting damage), they’re seen by some as a better alternative to antibiotics, which may kill not only harmful bacteria, but also certain helpful bacteria, possibly allowing more dangerous strains to take their place. That means synthetic mucin might offer a less intrusive alternative, used “not necessarily to resolve infections but to stabilize or prevent infection,” says Katharina Ribbeck, an assistant professor in the department of biological engineering at MIT, who co-authored the study with Erica Shapiro Frenkel, a Ph.D. student in her lab.

It’s possible that MUC5B encases S. mutans in “a 3-D spiderweb” that traps the acid they secrete.

Cavities form when bacteria like S. mutans cling to our teeth, forming an intricate, meshlike arrangement known as a biofilm. The bacteria that make up the biofilm feed on sugars from the food we eat to produce acid that can then dissolve the tooth enamel. To investigate how mucus might guard against this process, Ribbeck’s group got down to the molecular level and homed in on a mucin known as MUC5B. While that sounds like a covert government agency, it’s actually the most commonly found mucin in the mouth.

First the researchers isolated MUC5B from saliva samples of volunteers. Then they grew S. mutans bacteria with sugar and a special broth in plates containing wells that were made from a plastic often used to model a tooth’s enamel in lab experiments. Some wells also contained MUC5B. In the end, 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 wells containing MUC5B. That suggests the mucin somehow prevents S. mutans from sticking to the tooth surface.

How, exactly? The researchers aren’t sure, but it’s possible that MUC5B encases S. mutans in “a 3-D spiderweb” that traps the acid they secrete, Ribbeck says. MUC5B might also form a bacteria-repellent coating over the tooth surface, or even turn off S. mutans genes involved in attachment and biofilm formation. Ribbeck and Frenkel are still teasing out the most likely mechanism, though they also suspect that mucins might maintain bacterial diversity in the mouth by not only keeping S. mutans alive, but also neutralizing the toxins or other molecules that different bacterial strains release to outcompete each other.

Synthetic mucus could even be used to prevent food spoilage or biofouling.

Of course, scientists still need to confirm mucin’s protective role before they begin investigating the mechanisms involved. Ribbeck and Frenkel’s study was done in plastic wells — not on actual teeth in actual living animals. William Bowen, a professor emeritus at the University of Rochester’s School of Medicine and Dentistry, also points out that cavity-causing bacteria embed themselves in a gluey film that forms over the tooth, known as plaque — not directly to the tooth surface itself. And many other bacteria in the mouth cause cavities, not just S. mutans. “It’s not a major acid producer,” Bowen says.

Still, 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 be used to prevent, say, food spoilage or the accumulation of bacteria on ship hulls and other surfaces, a process known as biofouling. “The applications are enormous,” Ribbeck says.


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