Mucus acts as a protective barrier on wet epithelial surfaces in the body including the gastrointestinal, respiratory, and reproductive tracts. A main component of mucus is mucin, which give mucus its viscoelastic properties and is a key component of host defense at these epithelial interfaces. Altered mucin production has been linked to gastrointestinal diseases such as Crohn’s disease and respiratory illnesses like cystic fibrosis, which highlights the importance of regulated mucin production.

Although the role of mucins in gastrointestinal and respiratory illnesses has been well characterized, little is known about how salivary mucins protect the oral cavity from common diseases such as dental caries. Streptococcus mutans is one of the primary bacteria that cause dental caries, which form when bacteria grow on tooth surfaces then produce organic acids as metabolic byproducts. The decrease in local pH leads to dissolution of tooth enamel then cavity formation. The research in this thesis uses purified human MUC5B salivary mucin to better understand how this mucin could play a role in the prevention of cavity formation. Results shown in Chapter 2 demonstrate that MUC5B significantly reduces S. mutans attachment and biofilm formation on glass and hydroxyapatite. In addition, MUC5B does not significantly reduce S. mutans viability indicating the decrease in S. mutans surface colonization is due to a shift in cells from the biofilm to the planktonic state. In Chapter 3, a dual-species competition model is used to study the effects of MUC5B in a more complex environment. The two species in the model are S. mutans and Streptococcus sanguinis, which are known to compete in the oral cavity. In this study, MUC5B increases S. mutans and S. sanguinis coexistence. The reduction in interspecies competition could be caused by an increase in the relative proportion of cells in the less competitive planktonic state, which occurs in the presence of MUC5B. Taken together, the results presented in this thesis indicate that MUC5B could play a key role in protecting the oral cavity from disease and in maintaining a healthy microbiota.