Hydroxylapatite beads as an experimental model to study the adhesion of lactic acid bacteria from the oral cavity to hard tissues.

The oral environment contains many different types of microorganisms, including both Gram-negative and Gram-positive cocci, bacilli, and spirochetes. From the ecological point of view, the oral cavity is a perfect niche for certain bacteria such as lactobacilli because they interact, forming different types of communities. Lactobacilli have been associated with the generation of caries in some reports, secondary to the cariogenic Streptococcus. In previous papers, the isolation and identification of 145 strains from healthy subjects and from subjects with active caries were performed. Strains were characterized by their surface properties and also by the production of inhibitory substances. From all the strains, one isolated from the teeth of healthy patients and another from a patient with caries, sharing some surface properties, were selected for further study of their adhesion properties in an experimental model by using hydroxylapatite beads. Adhesion is the first step in the association of microorganisms with surfaces or mucous membranes. The first approach is a nonspecific interaction of both surfaces; later some other types of interactions can occur, involving more specific mediators of adhesions. Many different assays are available to study the adhesion phenomenon; some of them use predictive characteristics, and others use experimental models resembling the in vivo situation. Two model systems predominate. The most widely used has been saliva-coated hydroxylapatite or hydroxylapatite coated with buffers, proteins, and other substances. In an attempt to increase knowledge of the mechanisms of adhesion of oral lactobacilli with hard surfaces, this chapter describes an experimental model for studing the adhesion between lactobacilli and hard tissues represented by hydroxylapatite, the component most abundant in the teeth. The following steps were performed: 1. Obtaining the microorganisms. 2. Preparation of the hydroxylapatite beads. 3. Adhesion assay.