Bactericidal and anti-biofilm properties against Streptococcus mutans and Streptococcus sobrinus of rhinacanthin-C isolated from Rhinacanthus nasutus

Abstract

Although chlorhexidine (CHX) is commonly used as a standard antiseptic treatment in the oral cavity, its potent cytotoxicity on human periodontal tissues has been reported. Natural anti-biofilm medications could be therefore used as alternatives. In this study, the anti-bacterial and anti-biofilm activities of rhinacanthin-C (Rh-C) isolated from Rhinacanthus nasutus were determined against Streptococcus spp. (S. mutans and S. sobrinus), responsible for dental caries or tooth decay. RhC showed strong inhibitory and bactericidal effects against both tested species. The minimum inhibitory concentration (MIC) and minimum bactericidal concentration (MBC) values for S. mutans were 4 and 8 μM, respectively, and the MIC and MBC for S. sobrinus were 2 and 4 μM, respectively. As expected, 0.12 % (w/v) CHX, being a concentration present in commercial mouth rinses, showed a complete inhibition on biofilm formation and a decrease in the bacterial biomass in the formed biofilms, shown by biofilm formation assay and confocal laser scanning microscopy, respectively. Likewise, Rh-C showed concentration dependent (0-32 µM) anti-adherent property of both streptococci on biofilm formation and a decrease in the bacterial biomass in the formed biofilms. Interestingly, the effective anti-biofilm concentrations of Rh-C did not have cytotoxic effects on human gingival fibroblast (HGF) cell viability, whereas incubation with 0.12 % (w/v) CHX decreased HGF cell viability to approximately 25 %. The results suggest the potential use of natural-based Rh-C (up to 32 µM) as an effective anti-bacterial and anti-biofilm agent in oral topical rinses or toothpastes for prevention of caries.

Keywords

• bacterial biofilm
• dental caries
• natural-based anti-bacterial
• natural-based anti-biofilm agent