Fungal inhibition by Manuka honey and synergists

Abstract

Superficial and cutaneous fungal infections are mostly caused by the dermatophytes and commensal yeasts. Despite of their medical significances, standardised testing methods against some fungal skin pathogens are not developed yet. New Zealand manuka honey previously showed significant nonperoxide antifungal activity against some of fungal skin pathogens, however the disease is notoriously difficult to treat; it is probable that antifungal drug synergism can be utilised. The concept of antifungal treatment synergies have been previously explored as membrane perturbation, resulting in increasing fluidity, it is likely this effect would promote the uptake of the antifungal agents present in the honeys. Therefore the general objective of this study was to screen a range of different honeys in combination with iron chelators (lactoferrin and cavortin), and manuka essential oil by in vitro standardised methods against a group of medically significant fungal species; consequently, the antifungal potential of the honeys were analysed. Broth microdilution- and agar dilution antifungal susceptibility testing methods were set up and employed to screen manuka and two control honeys (kanuka and clover) against two yeasts, Candida albicans and Malassezia furfur, and three dermatophytes, Trichophyton rubrum, Epidermophyton floccosum and Microsporum gypseum; catalase (2 mg/ml) was added to remove H2O2 for analysis of the non-peroxide antifungal activity. Throughout the experiments C. albicans was observed as the most tolerated species to the antifungal activity of the honeys whilst M. furfur was the most susceptible species amongst the fungi tested. Once manuka honey was determined as the most efficient non-peroxide antifungal honey, the antifungal drug synergies with the potential synergists were analysed in a presence of catalase (2 mg/ml) against T. rubrum and C. albicans. Selected doses of manuka essential oil and manuka honey synergistically interacted against the growth inhibitions of T. rubrum (0.16 and 0.32 μl/ml) and C. albicans (2.5 and 1.25 μl/ml). However, 3 and 6 mg/ml lactoferrin were shown to interact with catalase treatment positive manuka honey synergistically to the growth inhibition of C. albicans, whilst selected cavortin concentration (1 mg/ml) showed a significant drug synergism against the growth of T. rubrum .