Aloe species are amongst the most ancient medicinal plants and their medicinal properties have been recorded throughout history. Aloes are indigenous to Africa, the Arabian Peninsula and their adjacent islands. The name [email protected] and the laxative ingredient aloin is said to be derived from an Arab term meaning shiny, very bitter substance from the leaves. The indigenous peoples of South Africa independently discovered the medicinal use of aloes. In addition to the many uses to which the Bitter Aloe (Aloe ferox), an indigenous species to South Africa, was put by the KhoiSan, other groups, such as the Xhosas, Zulus and Coloureds used other Aloe species for medicinal purposes. AAloe [email protected], in particular, is believed to have antifungal effects, but limited scientific information exists on the in vitro antifungal activity of this substance against dermatophytic fungi and yeasts that causes skin infections in humans. The antifungal activity of aloe gel containing five different concentrations, i.e. 0.25%, 1.0%, 1.5%, 2.0% and 2.5% of aloe bitters, was evaluated against two dermatophytes causing tinea pedis (athletes foot), i.e. Trichophyton mentagrophytes and Trichopyhton rubrum and the yeast, Candida albicans, which causes thrush. A non-dermatophyte, Fusarium verticillioides, was also included. All experiments were done in triplicate using an agar-diffusion method and included a negative (water) and two positive controls (Amphotericin B and Itraconazole E-tests). Both F. verticillioides and C. albicans showed resistance to all the concentrations used, except for two strains of the latter that showed very slight sensitivity at a concentration of 0.25% (mean inhibition zones of 1-2 mm). Both T. mentagrophytes and T. rubrum showed resistance at the higher concentrations (mean inhibition zones of 1-1.5 cm), but were sensitive to very sensitive to the lower concentrations (mean inhibition zones of 1.5-2.5 cm). All the T. rubrum strains were more sensitive than the T. mentagrophytes strains. As expected, the water did not inhibit the fungal growth, while all the fungi tested were sensitive to itraconazole at varying minimum inhibition concentrations (MIC). The MIC=s for amphotericin B also varied according to the strains tested. Resistance at higher concentrations and sensitivity at lower concentrations of aloe bitters are not easily explained. It can only be assumed that at the higher concentrations of the gel product, the bioavailability of the aloe bitters becomes less, hence the appearance of resistance. Therefore, C. albicans will be tested at concentrations lower than 0.25% of aloe bitters in order to establish possible sensitivity. It can provisionally be concluded that the antifungal activity of products containing aloe bitters is not only historical or anecdotal, but that these products in fact have in vitro antifungal activity against fungi causing athletes foot.
Full conference title:
The 15 th Congress of the International Society for Human and Animal Mycology
- ISHAM 15th (2003)