What's the News: The bacterial hordes that call your mouth home---and yes, even if you brush rigorously, you've got 'em---are generally a pretty benign bunch. Mostly they just mooch around, snagging tastes of whatever you're eating, but Streptococcus mutans
, the bad boy that causes cavities, releases tooth-corroding acid whenever you eat sugar. Even mouthwash that kills everything it touches can't save you from the ravages of S. mutans in the long term; it just grows back, along with the rest of your bacteria. Scientists who study the mouth microbiome
, however, think that a mouthwash that kills S. mutans and leaves the rest of the bacteria to take over S. mutans's real estate could spell the end of cavities. In a small clinical study
last year, one team found that one application of the mouthwash knocked down S. mutans levels, and that harmless bacteria grew back in its place. If the mouthwash pans out, it could join the ranks of an emerging new type of treatment: better living through hacking the microbiome. How the Heck:
The team, whose work is funded by toothpaste manufacturer Colgate-Palmolive, had designed a molecule called C16G2 that had been proven to kill S. mutans in Petri dishes. C16G2 is what's called an antimicrobial peptide---it seeks out a particular type of bacteria and inserts itself in or attaches itself to the cell membrane, causing the bacterium to self-destruct.
To see whether C16G2 would work in an actual mouth, they first crafted 12 plastic retainers for volunteers to wear that had slots to hold chips of enamel taken from cow teeth. (This provided a way to see if tooth enamel was eroded by the acid S. mutans secretes; grinding volunteers' actual teeth to check for enamel hardness would be frowned upon.)
After taking samples of the volunteers' baseline bacteria, the researchers had them swish with sugar water to get S. mutans active, and then had them swish once with a mouthwash containing C16G2. Over the next four days, they had the volunteers repeated the sugar water swishing and took samples of their mouth bacteria daily.
The researchers found that numbers of S. mutans in volunteers' mouths fell dramatically over the trial period, while in control tests without the C16G2 mouthwash, S. mutans populations grew. With the mouthwash, the cow enamel stayed hard, while in control tests, it softened.
Interestingly, the total number of bacteria in volunteers' mouths was about the same at the end of the study as at the start; "healthy" bacteria had moved in on S. mutans' turf. The researchers mention that previous studies have shown that once healthy bacteria have taken over all the territory in the mouth, S. mutans can have a hard time getting another foothold.
Not So Fast:
This study is so small that it's really only useful as a way to inform future, larger studies, and to ascertain that C16G2 doesn't fall totally flat at the first sight of a normal person's mouth. But it does pique the imagination.
What's the Context:
Treatments that manipulate humans' complement of bacterial hangers-on are getting a lot of attention these days. Though the idea of probiotics---substances or foods intended to replenish stores of "good" bacteria---has been around for a while, researchers are now starting to be able to study microbial communities in detail, thanks to advances in cheap and easy DNA sequencing.
But one of the most prominently reported-on treatments, fecal transplants, which attempt to treat imbalances in gut bacteria by administering bacteria from the feces of healthy people, is still a very new phenomenon. Determining how well they work, and how to do them safely, without giving patients diseases or giving them bacteria that clash with their genetic makeup, is something scientists and doctors are still working on. We don't even really know how eating yogurt affects gut bacteria.
It's worth keeping in mind, too, that what exactly a healthy microbiome is probably varies from person to person. A study last year indicated that people may fall into one of three gut microbiome types, analogous to blood types. The same could be true for the other colonies than call us home.
The Future Holds: The next step is to try a much larger experiment of similar design, and should that produce similar results, deal with these pressing questions: How long do the effects last? Can the newly healthy bacterial community withstand repeated attacks from S. mutans invaders? And how long would it take for S. mutans to develop a resistance?Reference: Sullivan, et al. Clinical Efficacy of a Specifically Targeted Antimicrobial Peptide Mouth Rinse: Targeted Elimination of Streptococcus mutans and Prevention of Demineralization. Caries Res. 2011; 45(5): 415–428. Published online 2011 August 19. doi: 10.1159/000330510
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