Growth Inhibitory Effects of Antimicrobial Natural Products against Cariogenic and Health-Associated Oral Bacterial Species.

PURPOSE: This study investigated whether selected natural products could specifically target the growth of a caries-associated bacterial species (Streptococcus mutans) without affecting the viability of a health-associated oral commensal bacterial species (Streptococcus sanguinis). MATERIALS AND METHODS: Agar diffusion assays were used to screen the natural products for bacterial-growth inhibitory effects and the diameters of the inhibitory zones for the two bacterial species compared. The minimum inhibitory concentrations (MIC) of the natural products that showed growth inhibitory effects were determined using the broth microdilution method. RESULTS: Except for the berry extracts (cranberry, wild blueberry, and strawberry), all the other selected natural products (peppermint, ginger, cinnamon, rosemary, liquorice, xanthorrrhizol, tt-farnesol, guaijaverin, and macelignan) exhibited varying degrees of bacterial growth inhibition. The MIC values ranged from as low as 4 µg/ml for xanthorrrhizol to 1000 µg/ml for guaijaverin. All the growth inhibitory natural agents tested showed similar inhibition for both S. mutans and S. sanguinis. CONCLUSIONS: Although several natural products exerted significant antibacterial effects, none had selective inhibitory action on the growth of S. mutans.

Polyphenol-Rich Cranberry Extracts Modulate Virulence of Streptococcus mutans-Candida albicans Biofilms Implicated in the Pathogenesis of Early Childhood Caries.

Purpose: The purpose of this study was to investigate the effects of polyphenol-rich cranberry extracts on dual-species Streptococcus mutans-Candida. albicans biofilms implicated in contributing to the severity of early childhood caries. Methods: S. mutans-C. albicans biofilms were grown on saliva-coated hydroxyapatite discs (s-HA) mounted on the high-throughput Amsterdam Active Attachment model. The s-HA discs were treated with the cranberry extracts/vehicle control for five minutes just before biofilm growth and subsequently, for similar exposure times, after 12 hours and 24 hours of biofilm growth. The treated 24-hour-old biofilms were then assessed for acidogenicity, metabolic activity, exopolysaccharide (EPS)/microbial biovolumes, structural organization, and colony forming unit (CFU) counts. Results: Treatment with 500 to 1,000 µg/mL of the cranberry extracts produced significant reductions in acidogenicity and metabolic activity (P<0.0001) compared to the control-treated biofilms. A significant decrease in biovolumes of the EPS (P=0.003) and microbial biofilm components (P=0.007) was also seen. Qualitative assessment of confocal biofilm images revealed that the cranberry extract disrupted biofilm structural architecture. Finally, significantly fewer S. mutans (P=0.006) and C. albicans (P=0.036) CFUs were recovered from the cranberry-treated biofilms than from the control-treated bio-films. Conclusions: Cranberry extracts inhibited cariogenic virulence properties of S. mutans-C. albicans dual-species biofilms in an in vitro model.