Mucus - part of the 0.5% of saliva that is not water - contains salivary mucins, compounds that actively protect teeth from damage by the cavity-causing bacterium Streptococcus mutans, according to a new study.
Previously it was thought that salivary mucins - large glycoproteins - did little more than keep mucus in saliva slippery and elastic, contributing to its gel-like properties. But now it seems they play an active role in defending against pathogens and keeping the human microbiome healthy.
S. mutans causes tooth decay by first attaching itself to teeth by forming a biofilm from sticky polymers that it produces. As the bacterium grows under the protection of the biofilm, organic acid byproducts of its metabolism attack the tooth enamel, causing cavities.
For their study, the researchers focused on how the salivary mucin MUC5B affects the ability of S.mutans to attach to teeth and form a biofilm. These are the two key steps necessary for cavities to form, Frenkel explains.
The investigation grew out of previous work looking at gastric mucins in pigs that protected against lung pathogens. The researchers wondered if salivary mucins might also play a protective role.
Frenkel says common diseases like cystic fibrosis, ulcerative colitis and asthma have been linked to problems with mucin production.
"There is increasing evidence that mucins aren't just part of the mucus for structure or physical protection, but that they play an active role in protecting the host from pathogens and maintaining a healthy microbial environment," she adds.