Antifungal activity of epithelial secretions from selected frog species of South Africa

Resistance to antibiotics has been acknowledged as a major global public health problem. The use of antimicrobial peptides to provide alternatives to combat multi-drug antibiotic resistance is beginning to attract increasing attention. The high diversity of amphibian skin peptides renders anurans an important potential source for the discovery of novel pharmacophores. This study aimed to investigate the antifungal activity of skin secretions from selected frogs (Amietia fuscigula, Strongylopus grayi and Xenopus laevis) and one toad (Amietophrynus pantherinus) of the south Western Cape Province of South Africa. Initially, different extraction techniques for the collection of skin secretions were tested and optimized, thereafter the extracts were tested against three fungal species of medical and agricultural importance that is, Candida albicans, Fusarium verticillioides and Aspergillus flavus. Chemical stimulation gave the best yield by mass, and secretions from A. fuscigula showed the best activity with an MIC of 40 μg / ml against C. albicans and 200 μg / ml against A. flavus. In general, C. albicans and A. flavus were the most sensitive while F. verticillioides was the most resistant. From this study it appears that bioprospecting of South African frog species has the potential to yield potential therapeutic lead agents.Key words: Antifungal, African anurans, antimicrobial peptides (AMP), Candida albicans, Aspergillus flavus, bioprospecting, minimum inhibitory concentrations (MIC)

ANTIMICROBIAL ACTIVITY OF STILBENOIDS AND FLAVONOIDS FROM THREE SPECIES OF COMBRETACEAE

Four phenanthrenes, one of them new, were isolated from the fruit of Combretum hereroense and one from the leaves of C. collinum. Three of them were moderately active against Candida albicans, Mycobacterium fortuitum and Staphylococcus aureus in the microplate assay. Four bibenzyls, one of which is novel, two chalcones, three flavanones and a flavone, all previously unreported from Combretaceae, were isolated from the leaves of C. apiculatum Engl. & Diels and two were isolated from the leaves of C. collinum. Pinocembrin, one of the ten compounds from C. apiculatum, had good activity against S. aureus and excellent activity against C. albicans in agreement with literature reports

Antioxidant activity of some medicinal and dietary African vegetables

Seven medicinal and dietary plant species from Southern Africa were analysed for their antioxidant and total phenolic content. These were Lippia javanica, Tagetes minuta, Bidens pilosa, Vigna unguiculata, Amaranthus spinosus, Telfairia occidentalis and Corchorus olitarius. Aqueous methanol extracts were tested for free radical scavenging and anti-oxidant activity using three standard assays including 2,2′azinobis-(3-ethylbenzthiazoline-6-sulphonic acid) (ABTS), 1,1-diphenyl-2-picrylhydrazyl (DPPH) and ferric reducing antioxidant potential (FRAP). The Folin-Ciocalteu assay was used to determine the total phenolic content with gallic acid as a standard. The antioxidant activity of the plants ranged from 0.76 to 5.77 mmol TEAC/100 g (ABTS), 16.29 to 1711.22 mmol TEAC/100 g (DPPH) and 0.58 to 6.12 mmol TEAC/100 g (FRAP). B. pilosa and C. olitarius had the best activity in all assays, while V. unguiculata and A. spinosus were the least active. The total phenolic content ranged from 19.79 to 333.56 mg gallic acid equivalent (GAE)/100 g. In general, there was a good correlation between antioxidant activity and total phenolic content. These results imply that these plant species may possess health promoting effects and might be potential sources of potent natural antioxidants

Fusarium inhibition by wild populations of the medicinal plant Salvia africana-lutea L. linked to metabolomic profiling

Publication of this article was funded by the Stellenbosch University Open Access Fund.The original publication is available at http://www.biomedcentral.com/1472-6882/14/99Abstract Background: Salvia africana-lutea L., an important medicinal sage used in the Western Cape (South Africa), can be termed a ‘broad-spectrum remedy’ suggesting the presence of a multiplicity of bioactive metabolites. This study aimed at assessing wild S. africana-lutea populations for chemotypic variation and anti-Fusarium properties. Methods: Samples were collected from four wild growing population sites (Yzerfontein, Silwerstroomstrand, Koeberg and Brackenfell) and one garden growing location in Stellenbosch. Their antifungal activities against Fusarium verticillioides (strains: MRC 826 and MRC 8267) and F. proliferatum (strains: MRC 6908 and MRC 7140) that are aggressive mycotoxigenic phytopathogens were compared using an in vitro microdilution assay. To correlate antifungal activity to chemical profiles, three techniques viz. Gas chromatography-mass spectrometry (GC-MS); Liquid chromatography-mass spectrometry (LC-MS) and 1H Nuclear Magnetic Resonance (NMR) were employed. Principal Component Analysis (PCA) was applied to the NMR data. The partial least squares-discriminant analysis (PLS-DA) was used to integrate LC-MS and NMR data sets. All statistics were performed with the SIMCA-P + 12.0 software. Results: The dichloromethane:methanol (1:1; v/v) extracts of the plant species collected from Stellenbosch demonstrated the strongest inhibition of F. verticillioides and F. proliferatum with minimum inhibitory concentration (MIC) values of 0.031 mg ml-1 and 0.063 mg ml-1 respectively. GC-MS showed four compounds which were unique to the Stellenbosch extracts. By integrating LC-MS and 1H NMR analyses, large chemotype differences leading to samples grouping by site when a multivariate analysis was performed, suggested strong plant-environment interactions as factors influencing metabolite composition. Signals distinguishing the Stellenbosch profile were in the aromatic part of the 1H NMR spectra. Conclusions: This study shows the potential of chemotypes of Salvia africana-lutea in controlling fungal growth and consequently mycotoxin production. Products for use in the agricultural sector may be developed from such chemotypes.Stellenbosch UniversityPublishers' Versio