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Researchers sequence rare bacterium that causes rampant dental caries

By Dental Tribune International
August 16, 2018

URBANA, Ill., U.S.: Among the most prevalent chronic diseases in both children and adults is dental caries, which occurs when the mouth is in a state of dysbiosis. Up until now, little was known about the bacterium Streptococcus sobrinus, which accelerates caries in some people. However, a research team from the Department of Engineering from the University of Illinois at Urbana-Champaign has now successfully sequenced the complete genomes of three strains of S. sobrinus.

Since S. sobrinus is difficult to work with in the laboratory and it is not present in all people, researchers have instead focused their efforts on understanding the more stable and prevalent Streptococcus mutans, which was sequenced in 2002, according to research assistant professor Dr. Paul Jensen from the Carl R. Woese Institute for Genomic Biology at the university.

“Although it is rare, S. sobrinus produces acid more quickly and is associated with the poorest clinical outcomes, especially among children,” said Jensen. “If S. sobrinus is present along with S. mutans, you’re at risk for rampant tooth decay, which means there’s some level of communication or synergy between the two that we don’t understand yet.”

Now that the S. sobrinus sequencing is complete, the research team is building computational models to better understand how the two bacteria interact and why S. sobrinus can cause such potent caries in combination with S. mutans. They have already confirmed that S. sobrinus lacks complete pathways for quorum sensing, which is the ability of bacteria to sense and react to nearby bacteria, and ultimately proliferate. “S. sobrinus doesn’t have a complete system to do this,” said Jensen. “We’re really curious to explore this further and find out what is missing and why.”

According to Jensen, S. mutans bacteria send out feelers in the form of a peptide to find out how many other S. mutans cells are nearby. Once the S. mutans cells reach a certain threshold, they attack, creating an imbalance in the oral microbiome and leading to rapid cavity formation.

“For the S. sobrinus field, this is groundbreaking work because the field was plagued by a lack of information. In 2018, it is surprising that we had a whole species [of bacteria] that causes disease and no complete genome of it,” concluded Jensen.

This work was funded by a grant from the National Institutes of Health National Institute of Dental and Craniofacial Research and the Illinois Master of Engineering in Bioengineering program.

The study, titled “Complete genome sequences of Streptococcus sobrinus SL1 (ATCC 33478 = DSM 20742), NIDR 6715-7 (ATCC 27351), NIDR 6715-15 (ATCC 27352), and NCTC 10919 (ATCC 33402),” was published online in Microbiology Resource Announcements on July 26, 2018.

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