Development of new method for the eradication of etiological organism of dental caries using bovine milk containing antibodies against virulence factors of the organism and the adherence-inhibiting component.

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Bovine milk inhibits the saliva-induced aggregation of S. mutans. In this study, the milk component that possesses inhibitory activity against this aggregation was isolated and found to be lactoferrin. Surface plasmon resonance analysis indicated that bovine lactoferrin binds more strongly to salivary agglutinin than to recombinant PAc. To identify the saliva-binding region of bovine lactoferrin, 11 truncated bovine lactoferrin fragments were constructed. A fragment corresponding to the C-terminal half of the lactoferrin molecule had a strong inhibitory effect on the saliva-induced aggregation of S. mutans, whereas a fragment corresponding to the N-terminal half had a weak inhibitory effect. Seven shorter fragments corresponding to lactoferrin residues 473 to 538 also showed a high ability to inhibit the aggregation of S. mutans. These results suggest that residues 473 to 538 of bovine lactoferrin are important in the inhibition of saliva-induced aggregation of S. mutans.Next, the effect of bovine milk lactoferrin on S. mutans adherence to a salivary film was investigated. Bovine lactoferrin molecule and relatively long lactoferrin fragments containing residues 473-538 strongly inhibited S. mutans adherence to saliva-coated hydroxyapatite beads. Each cysteine residue in Lf411 (residues 473-538) was substituted by a serine residue, and the mutants Lf411-C481S and Lf411-C532S strongly inhibited S. mutans adherence. These results suggest that the functional domain of lactoferrin that binds to a salivary film lies in residues 473-538, and that the region might be concealed by disulfied bond formation between Cys481 and Cys532 in the Lf411 fragment.