Combinations of tt-Farnesol with Kaemferol and Quercetin against Streptococcus mutans-UA-159

Apis mellifera propolis contains tt-farnesol, quercetin, and kaemferol as potential antibacterial components. Objective: This study tested the hypothesis that the propolis component tt-farnesol provides a synergistic antibacterial action against Streptococcus mutans UA159 when combined with either kaemferol or quercetin. Methods: Tests for minimum inhibitory concentration (MIC) and minimum bacterial concentration (MBC) were performed according to NCCLS approved guidelines using S. mutans UA159. Bacterial concentration and optical density(540nm) were correlated using a growth curve.The original bacterial concentration was 5x10^5 CFU/mL in all assays. Using DMSO-ethanol (1:4) as the chemical solvent, the MIC was measured using 24-well plates and incubated at 37ºC in a 5% CO2 environment. The growth of Streptoccus mutans was confirmed by gram staining. The four controls for the MIC included: 1) solvent 2) 0.12%chlorhexidine 3) bacterial broth, and 4) solvent and bacterial broth. The three propolis components were tested at concentrations of 125, 250, 500 micromoles and replicated three times. In addition, tt-Farnesol was tested at 10, 50, and 100 mmoles and quercetin at 750, 1000, and 1250 micromoles. MBC was performed using blood-agar plates based on the MIC results. Results: The MBC and MIC of tt-Farnesol were 125 and 500 micromoles, respectively. Compared with the antibacterial activity of 0.12% chlorhexidine, kaemferol (500 micromoles) did not demonstrate bacterial inhibition, while quercetin showed an MIC of >1250 micromoles. When tt-Farnesol was combined in the same concentrations with either kaemferol or quercetin (125, 250, 500 micromoles), it did not show inhibition. Conclusion: Although the addition of quercetin and kaemferol to tt-Farnesol did not provide the anticipated antimicrobial synergistic effect at the concentrations tested, tt-farnesol exhibited good inhibition of S. mutans and one may consider it as a potential anticariogenic agent. This study was supported by NIH-NIDCR Grant DE 13412.