Formation of Interspecies Biofilms of Saccharomyces cerevisiae Yeast and Streptococcus thermophilus Bacteria Utilizing Co-flocculation

Introduction. Dental caries is one of the most prevalent dental diseases. The primary cause of this pathology is a disruption in the species composition of the oral microbiota. The main causative agent of caries is the bacterium Streptococcus mutans, which begins to dominate the pellicle of the teeth among representatives of its genus, secreting lactic acid that destroys the integrity of the enamel. The attachment of pathogenic microorganisms to dental plaque occurs, as with representatives of the normal flora, through proteins – lectins. This creates a prospect for introducing non-pathogenic, non-acid-producing microorganisms into the oral microbiome by artificially incorporating them into the pellicular microflora. The aim of this research is to develop a method for incorporating non-acid-producing microorganisms into the oral microbiome, based on the co-flocculation of yeasts and streptococci. Materials and methods. The yeast strains Saccharomyces cerevisiae I-224 and Saccharomyces boulardii were selected as non-acid-producing microorganisms. Streptococcus thermophilus var. lactis was used as a producer of the extracellular exp polysaccharide matrix for the common biofilm. Yeast biomass was cultivated in sterile grape must, while streptococcal biomass was grown in liquid YPD medium at 26°C for five days. Following separate cultivation of the lactic streptococcus and the wine yeasts, the cultures were decalcified via centrifugation at 4,000 rpm and treatment of the sediment with a 0.3 mol/l potassium oxalate solution. The precipitated microbial biomass was combined and subjected to flocculation by adding a 1.0% calcium chloride solution. The efficiency of co-flocculate formation was determined microscopically at a 900× magnification after staining the specimen with methylene blue. Results. The yeast Saccharomyces cerevisiae I-224 actively integrated into the common polysaccharide matrix, as evidenced by the clearing of the space around the co-flocculate and the absence of free streptococcal and yeast cells. The weakly flocculating probiotic yeast Saccharomyces boulardii scarcely formed unified flocculates with the bacteria. Discussion and conclusion. An original method has been developed for the creation of interspecies conglomerates of bacteria and yeasts united by a common exopolysaccharide matrix. This method opens the prospect of creating an oral probiotic that reduces the acid load on tooth enamel, as it allows for the partial replacement of acid-producing bacteria with agents of alcoholic fermentation.