Antimicrobial effect of medical-grade manuka honey against oral bacteria in vitro

Objectives: To assess the antimicrobial effect of manuka honey (Leptospermum scoparium) against oral microorganisms in order to explore its potential use in periodontal treatment.
Methods: Manuka (Comvita®, New Zealand) and white clover (Trifolium repens) honey (Hollands®, New Zealand), which served as a control honey, were compared for their minimum inhibitory concentration (MIC) and minimum bactericidal concentration (MBC) against four representative oral bacterial species. Honey was added to brain heart infusion (BHI), inoculated with the test microorganisms and incubated anaerobically at 37°C for 18 hours. MIC was determined by measuring optical density and MBC by spot-plating samples on BHI agar and incubating anaerobically.
Results: Both manuka and clover honeys inhibited growth of Streptococcus sanguinis and S. gordonii at 12.5% (w/v) and killed the bacteria at 25% (w/v) after 18 hours of incubation. S. mutans was resistant to both honeys at 50% (w/v), the highest concentration tested. Fusobacterium nucleatum (four strains) was killed after 4 hours incubation at 25% and 6% (w/v) for manuka and clover honeys, respectively.
Conclusions: Manuka honey was more effective than clover honey against three of the tested plaque-associated species. Subgingival application of manuka honey as an adjunct to periodontal treatment merits further investigation.However, since S. mutans was relatively resistant and pH of honey is below 5.5 this may predispose root surfaces to caries and erosion.