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)

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