GA 2017

Endophytes have been found in every plant species examined to date and have been recognized as potential sources of novel antimicrobials. The antimicrobial potential of endophytes isolated from South African medicinal plants have, however, been poorly explored. The aim of this study was therefore to investigate the antimicrobial activity of endophytes isolated from the roots of three popular South African medicinal plant species (Pelargonium sidoides, Hypoxis hemerocallidea and Gunnera perpensa) and explore the chemical diversity of the isolated endophytes. Fungal cultures were isolated from the roots, and extracts were prepared and tested independently and in combination with the host plant to determine if any synergistic interactions are apparent. Antibacterial studies were undertaken using the minimum inhibitory concentration (MIC) assay against Gram-positive (Staphylococcus aureus ATCC 25923 and Enterococcus faecalis ATCC 29212) and Gram-negative (Escherichia coli ATCC 8739 and Pseudomonas aeruginosa ATCC 27853) bacteria. A total of 19 endophytic fungi were isolated from the P. sidoides root. Four fungal extracts exhibited antibacterial activity either alone or in combination with the host plant. Noteworthy results were exhibited by a fungal isolate from Pelargonium sidoides root with a MIC value of 30 µg/mL against S. aureus and 60 µg/mL against E. coli. Six endophytic fungi could be isolated from the roots of H. hemerocallidea, and five from the roots of G. perpensa. Hypoxis hemerocallidea and G. perpensa both had one endophytic fungal strain that exhibited antibacterial activity against S. aureus with MIC values of 250 µg/mL and 500 µg/mL respectively. Results indicate that endophytic fungi from these South African medicinal plants yield a complex chemistry and could be a promising source of antimicrobial metabolites. Furthermore, selected species exhibit a synergistic antimicrobial role with the host plant demonstrating a unique anti-infective role for medicinal plants