Antimicrobial Peptide GH12 Suppresses Cariogenic Virulence Factors of Streptococcus mutans

Objectives: Cariogenic virulence factors of Streptococcus mutans include acidogenicity, aciduricity, and extracellular polysaccharides (EPS) synthesis. De novo designed antimicrobial peptide GH12 has shown bactericidal effects on S. mutans, but its interaction with virulence and regulatory systems of S. mutans remains to be elucidated. The objectives were to investigate the effects of GH12 on virulence factors of S. mutans, and further explore the function mechanism at enzymatic and transcriptional levels.
Methods: To avoid decrease in bacterial viability, we limited GH12 to subinhibitory levels. We evaluated effects of GH12 on acidogenicity of S. mutans by pH drop, lactic acid measurement and lactate dehydrogenase (LDH) assay, on aciduricity through survival rate at pH 5.0 and F₁F₀-ATPase assay, and on EPS synthesis using quantitative measurement, morphology observation, and structural analysis. Afterwards, we conducted quantitative real-time PCR to acquire the expression profile of related genes.
Results: GH12 at 1/2 MIC (4 mg/L) inhibited acid production, survival rate, EPS synthesis, and biofilm formation. The enzymatic activity of LDH and F₁F₀-ATPase was inhibited, and ldh, gtfBCD, vicR, liaR, comDE genes were significantly downregulated.
Conclusions: In conclusion, GH12 inhibited virulence factors of S. mutans, through reducing activity of related enzymes, downregulating virulence genes, and inactivating specific regulatory systems.