Fig. 1. The stepwise process of oral microbial colonization. 1) After secretion, a process almost exclusively governed by the autonomic nervous system, the salivary proteins form a pellicle on the host’s tissues. Typical constituents of this pellicle are the mucins (eg, MUC7) and various other secretory proteins such as lactoferrin, S-IgA, and -amylase. 2) Whereas this pellicle may form a barrier against colonization by some microorganisms, other microorganisms have the capacity to use this pellicle as a means to adhere to the tissues of the host. Examples of the latter are viridans streptococci such as S. sanguis and S. gordonii. 3) Adherence leads to the formation of an adhesive microbial layer that subsequently may promote colonization of other microorganisms through coadherence (ie, adherence among microbial species). The secretory proteins also play an important role in this coadherence by inhibiting some microbe-microbe interactions although promoting others. Inhibition of coadherence is caused when secretory proteins block microbial receptors, hereby preventing binding to other microorganisms. Promotion of coadherence may occur when two microbial species carry receptors for the same salivary protein; hereby these microbial receptors become "cross-linked" by their common salivary ligand.

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