Abstract:
BACKGROUND: Diseases caused by microorganisms and parasites remain a major challenge globally and particularly
in sub-Saharan Africa to man and livestock. Resistance to available antimicrobials and the high cost or unavailability
of antimicrobials complicates matters. Many rural people use plants to treat these infections. Because some
anthelmintics e.g. benzimidazoles also have good antifungal activity we examined the antifungal activity of extracts
of 13 plant species used in southern Africa to treat gastrointestinal helminth infections in livestock and in man.
METHODS: Antifungal activity of acetone leaf extracts was determined by serial microdilution with tetrazolium violet
as growth indicator against Aspergillus fumigatus, Cryptococcus neoformans and Candida albicans. These pathogens
play an important role in opportunistic infections of immune compromised patients. Cytotoxicity was determined
by MTT cellular assay. Therapeutic indices were calculated and selectivity for different pathogens determined. We
proposed a method to calculate the relation between microbicidal and microbistatic activities. Total activities for
different plant species were calculated.
RESULTS: On the whole, all 13 extracts had good antifungal activities with MIC values as low as 0.02 mg/mL for
extracts of Clausena anisata against Aspergillus fumigatus and 0.04 mg/mL for extracts of Zanthoxylum capense,
Clerodendrum glabrum, and Milletia grandis, against A. fumigatus. Clausena anisata extracts had the lowest
cytotoxicity (LC50) of 0.17 mg/mL, a reasonable therapeutic index (2.65) against A. fumigatus. It also had selective
activity against A. fumigatus, an overall fungicidal activity of 98% and a total activity of 3395 mL/g against
A. fumigatus. This means that 1 g of acetone leaf extract can be diluted to 3.4 litres and it would still inhibit the
growth. Clerodendrum glabrum, Zanthoxylum capense and Milletia grandis extracts also yielded promising results.
CONCLUSIONS: Some plant extracts used for treatment of parasitic infections also have good antifungal activity.
Because it is much easier to isolate antifungal compounds by bioassay guided fractionation, this approach may
facilitate the isolation of anthelmintic compounds from active plant extracts. The viability of this approach can be
tested by isolating the antifungal compounds and then determining its anthelmintic activity. Some of these plant
extracts may also be useful in combating fungal infections.
