Methods: Samples of dental plaque and tongue coating, obtained separately from the oral cavity of 56 healthy human subjects, were mixed and applied to MRS plate agar, LBS plate agar, and Mitis-Salivarius (MS) plate agar. As a result, 1600 strains of lactic acid bacteria were isolated. These isolates were then evaluated in vitro for the following: production of volatile sulfur compounds (VSC), which cause halitosis; production of water-insoluble glucan (WIG), which causes smooth surface caries; the level of adhesion to salivary-coated hydroxyapatite and human oral cavity-derived cells (HO-1-N-1 and HSC-3); antibacterial activity against periodontal bacteria such as Porphyromonas gingivalis ATCC 33277, Prevotella intermedia ATCC 25611, Aggregatibacter actinomycetemcomitans Y4, which produce substances that cause halitosis, and cariogenic bacteria such as Streptococcus mutans ATCC 25175 and Streptococcus sobrinus ATCC 33478.
Results: Out of 1600 strains, 241 showing low productivity of VSC and WIG were selected. Using 16S ribosomal RNA gene sequencing, most strains were identified as Streptococcus oralis, Streptococcus salivarius, Streptococcus mitis, Lactobacillus gasseri, Lactobacillus fermentum, and Lactobacillus crispatus. As a result, 50 oral strains (14 from the genus Lactobacillus and 36 from the genus Streptococcus) were selected. These strains showed high levels of adhesion to salivary-coated hydroxyapatite and human oral cavity-derived cells and growth inhibiting effects on oral pathogenic bacteria.
Conclusions: We selected 50 beneficial lactic acid bacteria strains from the oral cavity. The results of this study suggest that these bacteria may improve the oral flora and play a role as new probiotics by relieving halitosis and preventing periodontal diseases and caries.