University Archives

Background: Streptococcus mutans is a key contributor to dental caries due to its acidogenic and biofilm-forming properties. Probiotic formulations including Streptococcus oralis, S. uberis, and S. ratti have been explored as modulators of oral ecology, with some strains shown to compete with S. mutans. However, the timing and strain-specific effects of probiotics on S. mutans remain unclear.

Objective: This study evaluated the ability of individual probiotic strains, a probiotic mixture, and a commercial probiotic tablet to inhibit S. mutans biofilm formation, biofilm acidity, and colonization of orthodontic arch wires.

Methods: S. oralis, S. uberis, and S. rattus were isolated from a commercial oral probiotic tablet (ProBiora 3®) and identified by 16S sequencing. Biofilms were developed in artificial saliva with 0.5% sucrose, either by introducing probiotics 3 hours before or after inoculation with S. mutans ATCC 25175 or a GFP-labeled S. mutans derivative. Biofilm biomass was quantified using a crystal violet assay and the pH of biofilm supernatants was measured. Stainless steel arch wires were colonized as described above, and imaged by fluorescence microscopy to assess S. mutans-GFP colonization. Probiotic effects on S. mutans biofilms were assessed for statistical significance by the students’ T-test.

Results: Early introduction of S. oralis and S. uberis produced the strongest inhibition of S. mutans biofilms (40–70% reduction) and markedly reduced colonization on arch wires. When probiotics were added after S. mutans established a biofilm, S. rattus replaced S. mutans on arch wires. Final pH values of all biofilms remained <5.5, indicating probiotic acidogenicity in the presence of sucrose.

Conclusions: Probiotic inhibition of S. mutans biofilms is both strain- and timing-dependent. S. oralis and S. uberis showed the greatest antagonistic activity when introduced prior to S. mutans, highlighting their potential in caries-preventive. However, acid production by probiotic streptococci requires careful consideration in formulation design.