Two anti-staphylococcal triterpenoid acids isolated from Psiloxylon mauritianum (Bouton ex Hook.f.) Baillon, an endemic traditional medicinal plant of Mauritius

Psiloxylon mauritianum (Bouton ex Hook.f.) Baillon (PM) is a traditional medicinal plant used for the treatment and management of dysentery and common infectious diseases in Mauritius. Locally, the plant is orally administered in the form of a broth made with the young leaves for its curative properties. Though the traditional use of this plant had been documented in early ethnomedicinal surveys, it had however never been studied. This study thus endeavors at validating the traditional use of PM and purifying the active bioactive secondary metabolites responsible for any observed biological activity. The crude extract was assessed in vitro for growth inhibiting activity against several microbial strains using both the broth microdilution assay and bioautography. Additionally, the antioxidant activity was assessed using standard assays and the most active extract was submitted to bio-guided fractionation for further evaluation. PM was found to be both strongly antibacterial and antioxidant. The crude acetone extract as well as its subsequent preliminary tannin-less fractions was found to be markedly anti-staphylococcal. Lowest Minimum Inhibitory Concentrations (MICs) of 51. μg/ml and 19. μg/ml were recorded for the crude extract and the most polar preliminary tannin-less (20% methanol in dichloromethane) fraction of PM, respectively. On the other hand, the plant was found to be only weakly antifungal, inhibiting the growth of Candida albicans at 3.25. mg/ml. Consequently, PM extract was further fractionated and the fractions were tested on Staphylococcus aureus. Bioassay guided fractionation led to the isolation and identification of (2α, 3β)-dihydroxyurs-12-en-28-oic acid and (2α, 3β) 23-trihydroxy-urs-12-en-28-oic acid, commonly known as, corosolic and asiatic acid respectively for the first time from this endemic species of Mauritius. The present study thus clearly indicates that PM possessed substantial antimicrobial, in particular anti-staphylococcal activity which corroborates with its use in the traditional Mauritian pharmacopoeia as a plant having potential anti-infective properties. The results so far obtained further substantiate, not only, the importance of screening medicinal plants as reliable sources of lead molecules, but also provide additional credence to the traditional uses of such plant. © 2014 South African Association of Botanists.