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Salivary Mucin MUC5B May Limit S. Mutans Attachment and Biofilm Formation - Study

December 02, 2014 In new research on host-microbe interactions in the oral cavity,1 a Harvard-MIT research team found that salivary mucin MUC5B, in purified form, may reduce Streptococcus mutans surface attachment and biofilm formation by maintaining S. mutans bacteria in free-floating (planktonic) form, even in the presence of sucrose.  According to the researchers, the presence or absence of MUC5B in the oral cavity may influence a person’s susceptibility to dental caries, particularly if the mucin’s presence helps to inhibit the attachment and colonization of S. mutans, the primary microbial factor in the etiology of dental caries.  The study, published in the Applied and Environmental Microbiology journal, was featured in online articles by Medical News Today,2 Science Daily3 and other websites.

Salivary mucins are large glycoproteins that adhere to the oral mucosa and act as the primary gel-forming components of mucus.  Mucins lubricate intraoral tissues and protect the mouth’s epithelial lining from dessication and chemical or mechanical injury.  MUC5B is considered the primary mucin component of the enamel and mucosal pellicle,4 providing protective coatings for hard and soft tissues and helping with the formation of food boluses for swallowing.

The Harvard-MIT biologists first aimed to identify in vitro specific growth conditions where S. mutans attachment and biofilm formation are strongest.  They found that S. mutans adherence and biofilm formation occurred at their highest levels in the presence of sucrose rather than glucose.  The addition of just 1% sucrose was sufficient to enhance S. mutans attachment without MUC5B.  S. mutans use sucrose to develop sticky extracellular polymers known as glucans, which facilitate biofilm formation and adhesion to hard dental surfaces.

The researchers then used glass slides and discs made of hydroxyapatite (crystals of calcium phosphate that form the mineral structure of dental enamel) to evaluate the effects of sucrose, purified salivary MUC5B or methylcellulose on S. mutans attachment and biofilm formation.  Methylcellulose was used as a comparative, gel-forming compound that is similar to salivary mucin but with a less complex molecular structure.  

The study found that adding supplemental purified MUC5B did not reduce levels of S. mutans bacterial growth in the test samples, but the presence of purified human MUC5B resulted in decreased S. mutans attachment and colonization.  This was attributed to more S. mutans bacteria remaining in the planktonic phase, rather than forming biofilm and adhering to surfaces.  Based on these findings, the authors suggest that salivary mucin MUC5B may be effective in limiting S. mutans bacteria from forming an aggressive biofilm state on teeth.

Further research on salivary MUC5B’s composition and function in individuals is needed to clarify its relative effectiveness in reducing S. mutans colonization.  Adequate salivary flow and composition serve highly protective functions by maintaining a neutral oral pH, protecting oral tissues against invasion by microorganisms, remineralizing dental tissue, and facilitating swallowing and digestion.  It is well established that individuals with dry mouth have higher caries risk, less mucosal protection and reduced capacity to prevent bacterial colonization.  Learn more about the functions of salivary proteins and strategies for managing xerostomia in this recent report5 from the ADA Council on Scientific Affairs, which was published in the August 2014 issue of JADA.

Footnotes

1.    Frenkel ES, Ribbeck K.  Salivary mucins protect surfaces from colonization by cariogenic bacteria. Appl Environ Microbiol. 2014 Oct 24. pii: AEM.02573-14. [Epub ahead of print].  Available at: “http://www.ncbi.nlm.nih.gov/pubmed/?term=Frenkel+ES”.  Accessed November 18, 2014.

2.    Paddock C.  Saliva protects teeth against cavities more than we thought.  MedPageToday, November 12, 2014.  Available at: “http://www.medicalnewstoday.com/articles/285285.php”.  Accessed November 19, 2014.

3.    Salivary mucins play active role to fight caries (press release).  American Society for Microbiology.  November 11, 2014.  Available at: “http://www.sciencedaily.com/releases/2014/11/141111142239.htm”.  Accessed November 19, 2014.

4.    Gibbons HL et al.  What interactions drive the salivary mucosal pellicle formation?    Colloids Surf B Biointerfaces. Aug 1, 2014; 120(100): 184–192.  Available at: “http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4097378/”.  Accessed November 20, 2014.

5.    Plemons JM, Al-Hashimi I, Marek CL; American Dental Association Council on Scientific Affairs.  Managing xerostomia and salivary gland hypofunction: executive summary of a report from the American Dental Association Council on Scientific Affairs.  J Am Dent Assoc. 2014 Aug;145(8):867-73.


Additional Resources

MouthHealthy: Dry Mouth

 

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