Abstract:
Background and aims: Skin supports an ecosystem with thousands of microbes thriving on its surface, few species of most are harmful and some beneficial to the host. The skin protects the host from microbes which take advantage of the damaged skin barrier. Atopic dermatitis/eczema is a chronic, pruritic and itchy condition which affects over 20% of children worldwide, but may continue in adulthood. Over 90% of eczematous lesions have the presence of Staphylococcus aureus (S. aureus), where group A streptococcus (GAS) is present in over 60% cases co-colonized with S. aureus. The medicinal benefits of honey have been known to humans for centuries, of which manuka honey is the most widely researched honey for its antibacterial, wound healing and antioxidant properties. Manuka honey has a broad spectrum of antibacterial activity mainly due to the presence of methylglyoxal. Topical application of manuka honey has the potential to treat eczema. The current manuka honey product - Derma Cream marketed by Comvita NZ Ltd is understood to relieve symptoms of eczema. It has a 30% concentration of honey which makes the cream highly viscous and adhesive on topical application, decreasing patient compliance and its aesthetic value. The resource of available manuka honey is also limited and its demand is increasing. Therefore, the aim of this project was to investigate the antibacterial effect of manuka honey Derma Cream on human skin cells and human skin tissue colonized with S. aureus and GAS and to determine if a lower concentration of manuka honey in the cream could maintain the efficacy of the current Derma Cream. Methods: Models were designed for adherence and quantification of bacteria on human skin cell lines to mimic human skin and human skin tissue using bioluminescence imaging. The efficacy of Derma Cream with varying concentration of manuka honey (10% - 30%) was determined individually on S. aureus and GAS colonised on skin cells and skin tissue. The efficacy of manuka honey was also compared with its equivalent methylglyoxal solution and sugar solution. The cream was characterized for its rheology, effect on trans-epidermal water loss and stability profiles. Results and Discussion: The Derma Cream dilutions showed a mix of bacteriostatic and bactericidal effect on GAS and S. aureus colonised on both models, where it was possible to decrease the concentration of manuka honey in the cream while maintaining the efficacy. The medical grade manuka honey solutions showed a bactericidal effect on GAS and S. aureus in liquid culture and on cell culture models, where efficacy was maintained above 20%. Manuka honey solutions had an equal antibacterial effect to its equivalent methylglyoxal solution on both bacterial species, suggesting it was the main antibacterial compound in this honey. The rheology studies confirmed that the firmness and viscosity of the cream decreased with a decrease in the concentration of honey, while the adhesiveness remained unaffected hence a lower concentration of honey would have a prolonged contact time with the skin. Conclusion: This project has demonstrated that the co-cultured human skin cell lines model and human skin tissue model developed for adherence can be used to study the efficacy of topical antibacterial formulation in real time. The Derma Cream marketed by Comvita NZ Ltd. has shown an antibacterial effect on GAS and S. aureus colonised on human skin cells and human skin tissue. The results of this project found that a minimum of 20% manuka honey is required to maintain the efficacy of the current Derma Cream and which may improve the products aesthetic value for patients.