Effects of salivary agglutinins on biofilm formation by Streptococcus mutans

Objectives: Interactions between salivary agglutinin and P1 of Streptococcus mutans are essential for bacterial aggregation and sucrose-independent adherence to the tooth surface. The purpose of this study was to analyze the effects of fluid-phase and surface-adsorbed salivary agglutinin on biofilm maturation by S. mutans. Methods: We have examined saliva-induced aggregation and biofilm formation by S. mutans UA159, and derivative strains carrying mutations affecting the localization or expression of P1, in the presence of fluid-phase or adsorbed saliva or salivary agglutinin preparations. Results: Whole saliva- and salivary agglutinin-induced aggregation of S. mutans was adversely affected by loss of SpaP and sortase (SrtA), but not by loss of trigger factor (RopA). Fluid-phase salivary agglutinin and, to a lesser extent, immobilized agglutinin inhibited biofilm development by S. mutans in the absence of sucrose, and whole saliva was more effective at decreasing biofilm formation than salivary agglutinin. Inhibition of biofilm development by salivary agglutinin was differently influenced by particular mutations, with the SpaP-deficient strain displaying greater inhibition of biofilm development than the SrtA- or RopA-deficient strains. As expected, biofilm-forming capacities of all strains in the presence of salivary preparations were markedly enhanced in the presence of sucrose, although biofilm formation by the mutants was still not as efficient as the parental strain. Aeration strongly inhibited biofilm development and the presence of salivary components did not restore biofilm formation in aerated conditions. Conclusion: The results disclose a potent ability of salivary constituents to moderate biofilm formation by S. mutans and reveal both P1-dependent and P1-independent pathways affecting biofilm formation in the presence and absence of salivary constituents. This study was supported by a grant from NIH (DE13239).