In Vitro Evidence for the Efficacy of Manuka Honey and Its Components Against the Major Human Pathogenic Sporothrix Species

Abstract

Background/Objectives: While various clinical manifestations occur in sporotrichosis, cutaneous forms predominate. The recommended sporotrichosis treatment is itraconazole, an antifungal with certain restrictions. In recent years, the observation of reduced treatment effectiveness in some patients has arisen, possibly due to Sporothrix spp. resistance mechanisms. Consequently, there is a growing need for alternative therapeutic approaches. This study investigates the antifungal activity of manuka honey (MH) against pathogenic species of the genus Sporothrix. Methods: In this study, we assessed MH antifungal efficacy across concentrations ranging from 5% to 40% against 26 Sporothrix spp. isolates. In addition, its components were evaluated through chromatography and other in vitro techniques. Results: Minimum inhibitory concentrations of MH were found to be 15-40%, 10-15%, and 5-10% for Sporothrix brasiliensis, Sporothrix schenckii, and Sporothrix globosa, respectively. Purified methylglyoxal did not hinder Sporothrix growth. The MH antifungal potential was compromised through treatment with catalase or filtration through a 0.22 µm cellulose membrane. Chromatographic analysis of the volatile organic compounds (VOCs) present in MH identified 40 VOCs, including carbonyl compounds, alcohols, esters, aromatic hydrocarbons, heterocyclic compounds, terpenoids, and carboxylic acids. Additionally, two phenolic compounds were identified as potential markers for the authentication of MH, along with a disaccharide that may contribute to its antifungal activity. Conclusions: MH has demonstrated biological activity against the most significant Sporothrix species with pathogenic impact on humans. This suggests its consideration in future research endeavors focused on novel topical treatments for cutaneous sporotrichosis in both human and animal subjects.

Keywords: antifungal activity; honey; hydrogen peroxide; sporotrichosis; treatment.

Figure 1

Minimal inhibitory concentrations (MIC) of manuka honey UMF15+ against three clinically relevant Sporothrix species. The species S. brasiliensis is further categorized in two groups: wild-type (WT) and non-wild-type (nWT) strains, based on their susceptibility to conventional antifungal drugs. The violin plots depict the distribution, central tendency, and variability of the minimal inhibitory concentration of the manuka honey. Each symbol within the violins represents the individual MIC values for each strain. The dashed line inside violins indicates the median MIC, while the dotted lines represent the interquartile range. Statistical analysis (Kruskal–Wallis test followed by the Dunn’s multiple comparison test) revealed no significant differences among the MIC values of the four groups studied.

Figure 2

Manuka honey inhibits, but does not kill, Sporothrix spp. The left panels display the results of the inhibitory activity assay conducted with increasing concentrations of manuka honey ([MH]): 0%, 5%, 10%, 15%, 20%, 30%, and 40% v/v, tested against three reference strains. The right panels show the outcomes of the fungicidal activity assay, where a 5 µL aliquot from each well of the inhibitory assay was plated onto potato dextrose agar. Notably, all strains were able to grow at the highest manuka honey concentration tested, despite the inhibition observed. For all experiments, a sterility control (SC) was included, with no fungal inoculation. Images are representative of triplicate experiments.

Figure 3

Volatile composition of the manuka honey. The graphs depict the percentage of each chemical class of compounds in the sample evaluated by gas chromatograph coupled to mass spectrometry (A) and their concentration, in ng/g (B).