The Antimicrobial Properties of Honey.

Abstract

Honey has been recognized as an effective antimicrobial agent, being able to combat both gram positive and gram negative bacteria as well as being able to affect strains exhibiting antibiotic resistance. This is due to it containing various naturally occurring substances that alter the environment the bacteria is in to provide an inhospitable growth environment. As a result, it is being considered as a possible topical agent to use in lieu of topical antibiotics which are gradually being met with more resistance. For this experiment, a New Zealand Manuka honey, a Portuguese Carob honey, and a Scottish Heather honey were used. Staphylococcus aureus and Pseudomonas aeruginosa were tested alongside these honeys to determine the honeys antimicrobial effect. To investigate the antimicrobial action of the honey, 75% solutions were inoculated with the bacteria and viable plates were counted after incubation. Hypoosmotic shock was examined as a possible mode of action whereby 20% honey solutions inoculated with the bacteria were centrifuged and cells exposed to hypoosmotic shock afterwards before plates were spread and counted. The antimicrobial effects of azelaic acid and possibly synergy between it and the honeys was tested by solutions that did and did not contain azelaic acid were plated and incubated before being counted. Compositional analyses were also carried out on each honey. The results indicate that there is significantly reduced growth in 75% honey solutions compared to TSB controls with the sugar control being anomalous and showing less growth than the honey samples. S. aureus showed more growth than p. aeruginosa, but growth was still heavily reduced. The hypoosmotic shock experiment showed significant results with definitively reduced growth. However, p. aeruginosa showed a higher rate of survival, even showing growth when cultured with the sugar control. The Manuka honey appeared to impact s. aureus the most heavily. The addition of azelaic acid to sub-inhibitory concentrations of honey drastically decreased bacterial growth, showing a complete bactericidal effect when exposed to p. aeruginosa and s. aureus showing highly reduced growth across all samples, TSB and sugar control included. Compositional analyses found a mixture of colours, antioxidant content, total phenolic content, sugar content and pH, but the Carob was the only honey used that did not produce H2O2 despite it not performing any more poorly than the other honeys used.