The role of natural salivary defences in maintaining a healthy oral microbiota

Abstract

Objectives: To provide an update on our current understanding of how saliva and its various constituents directly and indirectly affect oral bacteria and thereby play a role in the modulation and maintenance of a healthy oral microbiota and also the associations with symbiosis and dysbiosis.

Methods: The search for biomedical literature on saliva and its antimicrobial activities (years 1966 to 2017) was conducted in PubMed, Embase and Web of Science databases.

Results: This review underlines that saliva plays an essential role in shaping and maintaining the ecological equilibrium of the resident oral microbiota. Saliva contributes to the formation of the salivary pellicle, which covers the oral hard and soft tissues, and thereby determines the initial adhesion and colonisation of microorganisms. Saliva facilitates clearance of dietary carbohydrates and microorganisms from the oral cavity, but also supplies bacteria with nutrients through enzymatic breakdown of dietary starch and proteins and salivary glycoproteins. In addition, saliva comprises proteins such as mucins, which block the adherence of certain microorganisms to oral surfaces through binding and aggregating mechanisms. Saliva also provides antimicrobial activity through numerous proteins and peptides including mucins, lactoferrin, lysozyme, lactoperoxidase, statherin, histatins and secretory immunoglobulin A.

Conclusions: A balanced oral microbiome is important for the maintenance of oral health and symbiosis. Conditions associated with salivary gland hypofunction, impaired oral clearance, low salivary pH and altered salivary composition, often lead to perturbation of the function and composition of the oral microbiome causing dysbiosis, and an associated risk of oral disease.

Clinical significance: Saliva plays a significant role in keeping the relationship between the host and oral microbiota in a symbiotic state. In conditions with salivary gland dysfunction, the natural balance of the oral microbiome is often disturbed, leading to dysbiosis and associated risks of gingivitis, caries and fungal infection.

Keywords: Amylase; Lactoferrin; Lysozyme; Oral microbiota; Peroxidases; Salivary mucins.