Abstract
Streptococcus mutans has been reported as a primary cariogenic pathogen associated with dental caries. The bacteria can produce glucosyltransferases (Gtfs) to synthesize extracellular polysaccharides (EPSs) that are known as virulence factors for adherence and formation of biofilms. Therefore, an ideal inhibitor for dental caries is one that can inhibit planktonic bacteria growth and prevent biofilm formation. Bergenia crassifolia (L.), widely used as a folk medicine and tea beverage, has been reported to have a variety of bioactivities. The present study aimed to explore the effect of B. crassifolia (L.) leaf extracts on the biofilm of Streptococcus mutans. The B. crassifolia (L.) leaf extracts showed inhibitory effects by decreasing viability of bacteria within the biofilm, as evidenced by the XTT assay, live/dead staining assay and LDH activity assay, and could decrease the adherence property of S. mutans through inhibiting Gtfs to synthesize EPSs. In addition, the reduced quantity of EPSs and the inhibition of Gtfs were positively correlated with concentrations of test samples. Finally, the MTT assay showed that the extracts had no cytotoxicity against normal oral cells. In conclusion, the extracts and sub-extracts of B. crassifolia leaves were found to be antimicrobial and could reduce EPS synthesis by inhibiting activities of Gtfs to prevent bacterial adhesion and biofilm formation. Therefore, B. crassifolia leaves have potential to be developed as a drug to prevent and cure dental caries.
Highlights
Dental caries is one of the most prevalent and costly infectious diseases in the world (Huang et al, 2016)
The minimal bactericidal concentration (MBC) values determined by the agar dilution method were shown to be 2 or 3 times higher than the minimal inhibitory concentration (MIC) values, which is consistent with a previous report indicating that the MBC values were typically two to four times higher than the MIC values (Song et al, 2006)
These results suggest that the extracts of B. crassifolia (L.) Fritsch leaves all exhibited inhibitory activities against S. mutans
Summary
Dental caries is one of the most prevalent and costly infectious diseases in the world (Huang et al, 2016). Cariogenic biofilms play an important role in the development of caries. They develop as pathogens accumulated on tooth surfaces, forming highly structured microbial communities that are tightly adherent and enmeshed in an extracellular matrix (Davies, 2003; Paes Leme et al, 2006; Chen et al, 2016). Within the complex oral microbiome, Streptococcus mutans is recognized as one of the primary pathogens of dental caries (Kaur et al, 2015). S. mutans is not always the most abundant organism among oral bacteria, it can rapidly orchestrate the formation of cariogenic biofilms (Bowen and Koo, 2011). S. mutans can produce at least three types of glucosyltransferases (Gtfs), GtfB, GtfC and GtfD, which can utilize dietary sucrose to synthesize extracellular polysaccharides (EPSs) (Bowen, 2002). The water-insoluble glucan binds the bacterium for attachment to the tooth surface, while the water-soluble glucan may supply a source of metabolizable carbohydrate for plaque bacteria if nutrients become limited (Jenkinson and Lamont, 1997; Cross et al, 2007)
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