Bioautography indicates the multiplicity of antifungal compounds from twenty-four southern African Combretum species (Combretaceae)

Abstract

Dried ground leaves of 24 Combretum spp were extracted with hexane, dichloromethane, acetone and methanol and analysed by bioautography to determine the number of antifungal compounds against five animal fungal pathogens (Candida albicans, Cryptococcus neoformans, Aspergillus fumigatus, Microsporum canis and Sporothrix schenckii). There was some similarity in the chemical composition of the non-polar components of extracts using extractants of varying polarity. Acetone extracted the most antifungal compounds from Combretum spp. Combretum spp. in the section Hypocrateropsis, C. celastroides ssp. celastroides and C. clelastroides ssp. orientale had 62 different antifungal zones of inhibition compared to the 7 to 8 of C. microphyllum and C. paniculatum in the Connivetaia section. C. collinum subspecies were not active against all the tested pathogens. C. neoformans was the most sensitive organism against all Combretum species, with 367 zones of inhibition using different TLC solvent systems and extracts. A. fumigatus was the most resistant (192 zones of inhibition). The antifungal activity and number of active antifungal compounds were high enough to consider the use of extracts for clinical application and to isolate antifungal compounds from the extracts. Based on the Rf values of the antifungal compounds determined using solvents of varying polarity, activity is not only be attributable to tannins found in Combretum extracts as was previously postulated.