Antimicrobial properties of honey and mode of action.

Abstract

Antimicrobial-resistant strains of bacteria are becoming increasingly prevalent. As Manuka honey is recognised as an alternative to antibiotic therapy for treating infections of wounds, it is important to assess other honey samples for their antimicrobial activity. It is also important to understand their mechanisms of action, and determine the components of honey that most significantly contribute to overall antimicrobial effectiveness. Identification of these factors may aid the design of standardised medical honeys. This study has demonstrated the antimicrobial effectiveness of a Scottish Heather honey, Manuka honey, and Carob honey at 75% concentration for inhibiting the growth of two wound-infecting strains of bacteria, Staphylococcus aureus and Pseudomonas aeruginosa. All honeys significantly inhibited the growth of bacteria compared to growth control of each culture (p < 0.05). Manuka honey was the most effective at inhibiting Staphylococcus aureus and Carob honey was the most effective at inhibiting Pseudomonas aeruginosa. Compositional analysis of these honeys has allowed for comparison of antimicrobial effectiveness to known antimicrobial factors, such as total phenolic content, pH, and sugar content. This study has also demonstrated that Staphylococcus aureus cells are significantly more sensitive to osmotic shock following culture in a sub-inhibitory dose of honey (p < 0.05), potentially showing cell wall damage as a mechanism of antimicrobial action of honey against this bacterium. Finally, this study has provided evidence that azelaic acid is an important contributor to the overall antimicrobial effectiveness of honey, by showing that the addition of a sub-lethal dose of azelaic acid significantly enhances the antimicrobial effectiveness of honey to a degree that is greater than either azelaic acid or honey alone (p < 0.05). This shows that azelaic acid should be considered for application in the production of standardised medical honeys. Keywords: honey; antimicrobial; osmotic shock; azelaic acid