Antimicrobial and Anti-caries Potential of Morin and Arginine against Oral Streptococcal Biofilms

The objective of this study was to evaluate the antimicrobial and synergistic effects of morin and arginine against oral biofilms, assessing their impact on bacterial viability, biofilm formation, and pH modulation. The minimum inhibitory concentration (MIC) and minimum biofilm inhibitory concentration (MBIC) were determined for S. mutans GS5, S. sobrinus AT33478, and S. sanguinis KCTC3284. Biofilm biomass was measured by crystal violet staining, and biofilm acidity was monitored by pH measurements. Confocal laser scanning microscopy (CLSM) was utilized to assess bacterial viability and extracellular polysaccharide (EPS) formation, while scanning electron microscopy (SEM) was employed to examine morphological changes. The MIC of arginine was 2.5% for S. mutans and S. sanguinis, and 5% for S. sobrinus; no measurable MIC was observed for morin. The MBIC of arginine was 2.5% for S. mutans, and 1.25% for S. sobrinus and S. sanguinis, while morin exhibited an MBIC of 250 μg/mL. Both morin and arginine increased biofilm pH dose-dependently. The combination of morin and arginine exhibited the most significant inhibition of biofilm formation (p < 0.05). CLSM and SEM were employed to verify the diminished bacterial biomass and EPS levels, with arginine exhibiting a particularly marked effect on EPS reduction (p < 0.05). Morin and arginine demonstrated synergistic antimicrobial effects against cariogenic biofilms, with arginine notably increasing biofilm pH and significantly reducing bacterial counts and EPS, indicating their potential as a natural anti-caries agent.