Activity of Ligustrum robustum (Roxb.) Blume extract against the biofilm formation and exopolysaccharide synthesis of Streptococcus mutans.

Ligustrum robustum (Roxb.) Blume is utilized as a traditional Chinese herbal tea with various health benefits and protective effects. Streptococcus mutans is an important cariogenic oral bacteria species. The present study aimed to assess the influence of Ligustrum robustum extract (LRE) on the biofilm formation of S. mutans and the mechanism of its action, as well as to identify its chemical components. For chemical identification, HPLC-MS and nuclear magnetic resonance were applied and four identified phytochemicals were reported (Ligurobustoside B, Ligurobustoside N, Ligurobustoside J, and Ligurobustoside C). The dose-dependent (0.5 to 2.0 µg/µL) antimicrobial toxicity of LRE against S. mutans biofilm formation and exopolysaccharide (EPS) synthesis was evaluated by confocal laser scanning microscopy (CLSM), Crystal violet stain, and CFU counting. The microstructure of S. mutans biofilm treated with LRE was investigated both on glass coverslips and ex vivo bovine dental enamel by scanning electron microscopy (SEM). Moreover, LRE downregulated the expression of S. mutans glucosyltransferase-encoding genes gtfB, gtfC, and gtfD, and the quorum sensing (QS) factors comD and comE, suggesting its toxic mechanism. In addition, the result of CCK-8 test on human oral cells revealed an acceptable biocompatibility of LRE. These findings indicated the possible application of this daily consumed herbal tea for caries prevention.

Utilization of the extract of Cedrus deodara (Roxb. ex D.Don) G. Don against the biofilm formation and the expression of virulence genes of cariogenic bacterium Streptococcus mutans.

ETHNOPHARMACOLOGICAL RELEVANCE: Cedrus deodara (Roxb. ex D.Don) G. Don is applied as anti-inflammatory and anti-infection agents in folklore medicine. AIM OF THE STUDY: The present study aimed to assess the antimicrobial activity of Cedrus deodara (Roxb. ex D.Don) G. Don extract (CDE) against Streptococcus mutans biofilm formation and its biocompatibility, as well as to identify its chemical components. MATERIALS AND METHODS: Confocal laser scanning microscopy (CLSM), crystal violet staining, and CFU counting assay were applied to investigate the effect of CDE on S. mutans biofilm formation and extracellular polysaccharides (EPS) synthesis. The microstructure of S. mutans biofilms formed on glass coverslips and bovine enamel treated with CDE was observed by scanning electron microscopy (SEM). qRT-PCR was used to measure the expression of virulence genes gtfB, gtfC, and gtfD, and zymogram assay was performed to investigate the enzymatic activity of Gtfs. Moreover, HPLC-MS and NMR were applied to identify its chemical components. CCK-8 assay was also performed on human oral cells to evaluate its biocompatibility. RESULTS: Under the treatment of CDE, S. mutans formed less biofilm on both coverslips and enamel surfaces and synthesized less EPS. Moreover, CDE downregulated the expression of gtf genes and inhibited the enzymatic activity of Gtfs. According to HPLC-MS and NMR results, molecular structures of six main compounds in CDE were identified. CDE also has a good biocompatibility. CONCLUSIONS: CDE exhibits inhibitory activity against S. mutans and a good biocompatibility. It has the potential to be developed as anti-caries agents for clinical use.