Antibacterial and anticandidal activity of <i>Tylosema esculentum</i> (marama) extracts

Abstract

Bean and tuber extracts of Tylosema esculentum (marama) -an African creeping plant -were obtained using ethanol, methanol and water. Based on information that T. esculentum is used traditionally for the treatment of various diseases, the antibacterial and anticandidal effects of tuber and bean extracts were investigated. The antimicrobial activity of the extracts was tested on methicillin-resistant Staphylococcus aureus (MRSA, ATCC 6538), Mycobacterium terrae (ATCC 15755), Corynebacterium diphtheriae (clinical) and Candida albicans (ATCC 2091). We performed the broth microdilution test for the determination of the minimum inhibitory concentration (MIC) and a method to determine survival of microorganisms after in vitro coincubation with the highest concentrations of T. esculentum extracts, followed by assessment of colony counts. Ethanol and methanol (phenolic) bean extracts exhibited higher potency against bacteria and yeast than aqueous extracts. Marama bean seed coat crude ethanolic extract (MSCE) and seed coat polyphenolic fractions, especially soluble-bound fraction (MSCIB), were highly antimicrobial against M. terrae, C. diphtheriae and C. albicans. All marama bean polyphenolic fractions, namely cotyledon acidified methanol fraction (MCAM), seed coat acidified methanol fraction (MSCAM), cotyledon insoluble-bound fraction (MCIB), seed coat insoluble-bound fraction (MSCIB), cotyledon-free polyphenolic fraction (MCFP) and seed coat free polyphenolic fraction (MSCFP) had high antimicrobial effects as shown by low respective MIC values between 0.1 mg/mL and 1 mg/mL. These MIC values were comparable to those of control antimicrobials used: amphotericin B (0.5 mg/mL) and cesfulodin (0.1 mg/mL) against C. diphtheriae, streptomycin (1.0 mg/mL) and gentamicin (0.4 mg/mL) against M. terrae, and amphotericin B (0.05 mg/mL) against C. albicans. Marama seed coat soluble-esterified fraction (MSCS) had closer activity to that of cefsulodin against M. terrae. High amounts of phenolic substances, such as gallic acid, especially in the seed coats, as well as high amounts of phytosterols, lignans, certain fatty acids and peptides (specifically protease inhibitors) in the cotyledons contributed to the observed antibacterial and anticandidal activities. Marama extracts, especially phenolic and crude seed coat extracts, had high multispecies antibacterial and anticandidal activities at concentrations comparable to that of some conventional drugs; these extracts have potential use as microbicides.

Characterisation of phenolic acids, flavonoids, proanthocyanidins and antioxidant activity of water extracts from seed coats of marama bean [Tylosema esculentum] – an underutilised food legume

“…The other phenolic acids were homogentisic acid (MW = 168.14) and p-hydroxybenzoic acid (MW = 138.12). Both gallic acid and p-hydroxybenzoic acid have been reported in acidified methanol extracts from marama bean seed coats and the latter compound was the most abundant phenolic acid (Chingwaru et al, 2011). These phenolic acids have also been reported in other legumes.…”

“…A. Shreiber)] is a long lived perennial tuberous legume plant growing wild in the arid regions of Southern Africa, in Botswana, Namibia and South Africa but also occurs in Angola, Zambia and Mozambique (Holse et al, 2010). Although the bean has been an important food source for the people of the Kalahari Desert for centuries and it is widely consumed by the local people (Bower et al, 1988), it is largely an underutilized crop (Jackson, et al, 2011). The marama bean plant is drought resistant and has a potential for cultivation as a food crop (Bower et al, 1988).…”

“…The seed coats have been found to contain phenolic acid and flavonoid compounds (Chingwaru, et al, 2011). Therefore, the seed coats may be used as raw material for the extraction of value added natural antioxidants for exogenous use as functional food ingredients with potential health benefits.…”

Therapeutic and Prophylactic Potential of Morama (Tylosema esculentum): A Review

“…Tylosema esculentum beans are believed to be superior in composition to soya beans (Biesele and Murray, 1983). The cotyledons consist of proteins (29-39%) and oil, mainly mono-unsaturated and di-unsaturated fatty acids (24-48%) and a number of phenolic compounds (Chingwaru et al, 2011a) but are devoid of cholesterol (Takundwa et al, 2012). The oils of morama beans contain approximately 31% unsaturated fatty acids, particularly oleic acid and linoleic acid (Chingwaru et al, 2011a;Biesele and Murray, 1983).…”

“…1), known as morama in Setswana is a creeping plant (Fig. 2) that is native to the arid and semi-arid parts of Southern Africa including parts of Botswana, Namibia and South Africa (Chingwaru et al, 2011a(Chingwaru et al, , 2011b. The plant, which is underutilised and undomesticated, has maintained a central role in the diet and traditional medicines of the San and other indigenous populations of the region.…”