Abstract
Streptococcus mutans (S. mutans) has been proved to be the main aetiological factor in dental caries. Curcumin, a natural product, has been shown to exhibit therapeutic antibacterial activity, suggesting that curcumin may be of clinical interest. The objective of this study is to evaluate the inhibitory effects of curcumin on metabolism and biofilm formation in S. mutans using a vitro biofilm model in an artificial oral environment. S. mutans biofilms were treated with varying concentrations of curcumin. The biofilm metabolism and biofilm biomass were assessed by the 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl tetrazolium bromide assay and the crystal violet assay. Confocal laser scanning microscopy was used to analyse the composition and extracellular polysaccharide content of S. mutans biofilm after curcumin treatment. The biofilm structure was evaluated using a scanning electron microscope. The gene expression of virulence-related factors was assessed by real-time PCR. The antibiofilm effect of curcumin was compared with that of chlorhexidine. The sessile minimum inhibitory concentration (SMIC50%) of curcumin against S. mutans biofilm was 500 μM. Curcumin reduced the biofilm metabolism from 5 min to 24 h. Curcumin inhibited the quantity of live bacteria and total bacteria in both the short term (5 min) and the long term. Moreover, curcumin decreased the production of extracellular polysaccharide in the short term. The expression of genes related to extracellular polysaccharide synthesis, carbohydrate metabolism, adherence, and the two-component transduction system decreased after curcumin treatment. The chlorhexidine-treated group showed similar results. We speculate that curcumin has the capacity to be developed as an alternative agent with the potential to reduce the pathogenic traits of S. mutans biofilm.
Highlights
Dental caries, one of the most prevalent infectious diseases worldwide, is a biofilm-mediated, sugar-driven, multifactorial, dynamic disease [1]
The results showed that curcumin inhibited the growth of planktonic S. mutans with an minimum inhibitory concentration (MIC)
A common infectious disease worldwide, is caused by biofilm known as dental plaque that result from the adhesion of bacteria to tooth surfaces
Summary
One of the most prevalent infectious diseases worldwide, is a biofilm-mediated, sugar-driven, multifactorial, dynamic disease [1]. By adhering to solid surfaces, S. mutans can colonize the oral cavity and form a bacterial biofilm [7]. Dental biofilms are microbial aggregates encased in a self-produced extracellular polymer matrix. The phenotype of the bacteria involved in biofilm formation is quite different from the phenotype in the planktonic state [8]. The bacteria in a dental biofilm are far more resistant to unfavourable growth conditions, such as biocides and hydrodynamic shear forces [9, 10]. The extracellular polysaccharide (EPS) produced by S. mutans through glycosyltransferases (Gtfs) has been shown to form the matrix of the biofilm [11]. The EPS mediates the irreversible adherence between bacteria to form a high-celldensity biofilm [12], which increases the bacterial resistance to antibiotics
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