Antimicrobial synergy between cranberry and manuka honey against dental caries bacteria

Abstract

Dental caries is caused by dental plaque, which is a community of micro-organisms embedded in an extracellular polymer matrix as a biofilm on the tooth surface. Natural products that are widely accessible could be used as an alternative or adjunctive anti-caries therapy. Sometimes, when two products are used together, they yield a more powerful antimicrobial effect than the anticipated additive effect. These synergistic combinations are often better treatment options because individual agents may not have sufficient antimicrobial action to be effective when used alone. Cranberries contain phenolic compounds like anthocyanidins that disrupt biofilm formation by oral bacteria. Manuka honey has high concentrations of bioactive agents like methylglyoxal, which are cariostatic. Because cranberries and manuka honey have varied modes of antimicrobial action, it is important to test them for possible synergistic effects. Various cranberry extracts, manuka honey and methylglyoxal were subjected to agar well-diffusion assays in the presence of the bacteria Streptococcus mutans. By comparing the zones of inhibition around the wells containing individual extracts and also the extracts in combination, the most synergistic combinations were determined. Serial dilutions of these extracts were then added to a 96-well plate checkerboard assay. By finding the minimum inhibitory concentrations (MIC) and fractional inhibitory concentrations (FIC) synergy was determined. Synergy was demonstrated in two of the cranberry extracts tested with methylglyoxal, the bioactive agent in manuka honey. The synergistic combinations found in this research can be good candidates for a dentifrice to inhibit the formation of dental plaque and avoid the development of caries.