Abstract
ABSTRACT Cariogenic virulence factors of Streptococcus mutans include acidogenicity, aciduricity, and extracellular polysaccharides (EPS) synthesis. The 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 mechanisms at enzymatic and transcriptional levels. 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, vertical distribution analyses and biomass calculation. Afterwards, we conducted quantitative real-time PCR to acquire the expression profile of related genes. 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, and comDE genes were significantly downregulated. In conclusion, GH12 inhibited virulence factors of S. mutans, through reducing the activity of related enzymes, downregulating virulence genes, and inactivating specific regulatory systems.
Highlights
Dental caries is a transmissible infectious disease caused by cariogenic bacteria, and Streptococcus mutans has been recognized as the principal etiological agent of dental caries [1]
We evaluated the effects of GH12 at sub-minimal inhibitory concentration (MIC) levels on basic viability of S. mutans by growth curves and MTT assay
Activity relationship studies by Giangaspero et al [36], we concluded that this poor efficacy may be related to that KSL does not adopt the optimal structure of cationic, amphipathic α-helical antimicrobial peptides (AMPs)
Summary
Dental caries is a transmissible infectious disease caused by cariogenic bacteria, and Streptococcus mutans has been recognized as the principal etiological agent of dental caries [1]. Cariogenic virulence factors of S. mutans lead to abundant acid production, acid tolerance and stable biofilm formation [2]. Aciduricity is a pivotal virulence factor of S. mutans. Membranebound F1F0-ATPase works as a pump to transport protons from cells and to maintain internal pH values. This is believed as the determinant of aciduricity of this bacterium [4]. Another critical virulence factor of S. mutans is its ability to produce glucosyltransferases (GTFs) to catalyze synthesis of intracellular polysaccharides (IPS) and extracellular polysaccharides (EPS) from sucrose [5]. Suppression of cariogenic virulence of S. mutans could be an appealing approach to preventing dental caries
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