Potent inhibition of dermatophyte fungi by Australian native jarrah honey

Abstract Poster session 1, September 21, 2022, 12:30 PM - 1:30 PM Objectives Honey has been used as a remedy for multiple ailments, and the antibacterial activity of many different floral honeys has been extensively explored. The capacity of honey to inhibit fungi is much less well understood. Here we investigate the inhibition of dermatophyte species by native Australian jarrah honey. Methods Jarrah honey was sourced from beekeepers and commercial suppliers. Artificial honey, made from glucose (22.9%), fructose (20.7%), and sucrose (1.6%), was used to control for osmolarity. Hydrogen peroxide production by honey was assessed using horseradish peroxidase (HRP)/ο-dianisidine colorimetric test. Dermatophytes included Microsporum canis, M. nanum, Nannizzia gypsea, Trichophyton interdigitale, T. rubrum, and T. tonsurans. Minimum inhibitory concentrations (MICs) and minimum fungicidal concentrations (MFCs) for honey were assessed using CLSI methods. Fluorescent and scanning electron microscopy were used to visualize the effect of honey on fungal conidia and hyphae. Results Jarrah honey inhibited all of the dermatophyte species with MICs ranging from 1.5-3.5% w/v, and MFCs from 2-5% w/v. No antifungal activity was seen with the artificial honey indicating this was not due to osmolarity. Microscopy revealed honey treatment prevented the germination of conidia and caused hyphae to bulge and collapse. While the inhibitory action of jarrah honey was greatly reduced by the addition of catalase suggesting hydrogen peroxide production was responsible for inhibition and killing, microscopy revealed hyphae were still damaged suggesting there are agents within honey that augment antifungal activity. REDOX fluorophores failed to detect internal oxidative stress within hyphae, indicating that damage likely occurs on the hyphal surface. Conclusion Jarrah honey is a non-toxic agent that may have utility in the treatment of superficial fungal infections caused by dermatophyte fungal species.