Background. Topical application of manuka honey is effective in the treatment of burns and soft-tissue infections. The aim of this study was to assess the antibacterial activity of manuka honey against plaque-associated bacteria in vitro in order to evaluate the potential application as an adjunct to periodontal treatment. Materials and Methods. The minimum bacteriostatic and bactericidal concentrations (MIC and MBC) of manuka honey were compared to those of white clover honey against a variety of plaque-associated bacteria, at the natural and neutral pH. Dissolved calcium was measured following incubation of honeys with hydroxyapatite (HA) beads to assess their potential to demineralise oral hard tissues. Results. Both honeys inhibited most tested oral bacteria at similar MIC/MBC, but Streptococcus mutans was comparatively resistant. The honeys at pH neutral had little effect on antimicrobial activity. Incubation of HA beads in honey solutions resulted in pH-dependent calcium dissolution, and inoculation with S. mutans promoted further demineralisation by both types of honey. Conclusion. Manuka honey is antimicrobial towards representative oral bacteria. However, the relative resistance of S. mutans in association with the high concentrations of fermentable carbohydrates in honey and the direct demineralising effect at natural pH mitigate against the application of honey as an adjunct in the treatment of periodontal disease.
Manuka oil, an essential oil derived from the Leptospermum scoparium, has been traditionally used for wound care and as a topical antibacterial, antifungal, and anti-inflammatory. However, the essential oil is not well retained at mucosal sites, such as the oral cavity, where the benefits of the aforementioned properties could be utilized toward the treatment of persistent biofilms. Within this study, L. scoparium essential oil was incorporated into a semisolid emulsion for improved delivery. The safety profile of L. scoparium essential oil on human gingival fibroblasts was determined via cell viability, cytotoxicity, and caspase activation. The minimal bactericidal concentration of L. scoparium essential oil was determined, and the emulsion's antibiofilm effects visualized using confocal laser scanning microscopy. L. scoparium essential oil demonstrated a lower IC50 (0.02% at 48 h) when compared to the clinical control chlorhexidine (0.002% at 48 h) and displayed lower cumulative cytotoxicity. Higher concentrations of L. scoparium essential oil (≥ 0.1%) at 6 h resulted in higher caspase 3/7 activation, suggesting an apoptotic pathway of cell death. A minimal bactericidal concentration of 0.1% w/w was observed for 6 oral bacteria and 0.01% w/v for Porphyromonas gingivalis. Textural and rheometric analysis indicated increased stability of emulsion with a 1 : 3 ratio of L. scoparium essential oil: Oryza sativa carrier oil. The optimized 5% w/w L. scoparium essential oil emulsion showed increased bactericidal penetrative effects on Streptococci gordonii biofilms compared to oil alone and to chlorhexidine controls. This study has demonstrated the safety, formulation, and antimicrobial activity of L. scoparium essential oil emulsion for potential antibacterial applications at mucosal sites.