Bacteria Enlisted in Fight Against Cavities

Courtesy of the CDC/Dr. Richard Facklam.


Courtesy of the CDC/Dr. Richard Facklam.

Bacteria typically get the blame for causing tooth decay. But a previously unidentified strain of Streptococcus called A12 could help prevent it, according to researchers at the University of Florida College of Dentistry. Looking ahead, oral probiotic supplements based on A12 someday may be used to combat cavities.

Healthy mouths depend on neutral pH levels. When those levels become more acidic, cavities and other problems may follow. Earlier research had shown that urea and an amino acid known as arginine are broken down into ammonia, which helps neutralize acid in the mouth.

Also, research had shown that adults and children with few or no cavities were better at breaking down arginine than people with cavities. While the researchers knew that bacteria were responsible for breaking down these compounds, they needed to investigate which bacteria do it best and how they inhibit cavities.

“Like a probiotic approach to the gut to promote oral health, what if a probiotic formulation could be developed from natural beneficial bacteria from humans who had a very high capacity to break down arginine?” said Robert Burne, PhD, associate dean for research and chair of the college’s department of oral biology.

“You would implant this probiotic in a healthy child or adult who might be at risk for developing cavities,” Burne said. “However many times you have to do that—once in a lifetime or once a week—the idea is that you could prevent a decline in oral health by populating the patient with natural beneficial organisms.”

Streptococcus mutans metabolizes sugar into lactic acid, contributing to the acidic conditions in the mouth that dissolve enamel and cause cavities. But A12 neutralizes acid by metabolizing arginine in the mouth. It often kills S mutans as well.

“Also, if A12 doesn’t kill S mutans, A12 interferes with S mutans’ ability to carry out its normal processes that it needs to cause disease,” said Burne. “If you grow them together, S mutans does not grow very well or make biofilms, also known as dental plaque, properly.”

Marcelle Nascimento, DDS, PhD, an associate professor in the college’s department of restorative dental sciences, collected plaque samples for the study. She then isolated and screened more than 2,000 bacteria to characterize 54 bacteria that metabolized arginine.

“Out of these, A12 stood out for having all of the properties we were looking for in a bacteria strain that could prevent cavities in a probiotic application,” said Nascimento.

The researchers have sequenced A12’s entire genome and plan to turn their work into a risk assessment tool to screen for people who are at a higher risk for developing cavities, in combination with other factors such as diet and oral hygiene habits.

“If we can get to the point where we can confirm that people who have more of this healthy type of bacteria in the mouth are at lower risk of cavities, compared to those who don’t carry the beneficial bacteria and may be at high risk, this could be one of the factors that you measure for cavities risk,” Nascimento said.

Next, the researchers will look for more incidences of A12 in a larger sample of people and test how prevalent bacteria with similar properties are in the human mouth. Their work is supported by a 5-year, $3 million grant from the National Institutes of Health’s National Institute of Dental and Craniofacial Research.

The study, “Characterization of a Highly Arginolytic Streptococcus Species That Potently Antagonizes Streptococcus Mutans,” was published in Applied and Environmental Microbiology.

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