Evaluation of the antibacterial activity and toxicity of Terminalia ferdinandia fruit extracts

Introduction:Terminalia ferdinandiana is an endemic Australian native plant with a history of use as a food and as a medicinal agent by indigenous Australians. Yet the medicinal bioactivities of this plant are poorly studied. In the current study, solvent extracts from T. ferdinandiana fruit pulp were tested for antimicrobial activity and toxicity in vitro. Results: All extracts displayed antibacterial activity in the disc diffusion assay. The methanol extract proved to have the broadest specificity, inhibiting the growth of 13 of the 14 bacteria tested (92.9%). The deionised water extract inhibited the growth of 11 of the 14 bacteria tested (78.6%). The ethyl acetate, chloroform and hexane extracts inhibited 21.4%, 28.6% and 14.3% respectively. T. ferdinandiana methanolic extracts were approximately equally effective against Grampositive (100%) and Gram-negative bacteria (90%). All other extracts were more effective at inhibiting the growth of Gram-positive bacteria. The water, ethyl acetate, chloroform and hexane extracts inhibited the growth of 100, 50, 50 and 50% Gram-positive bacteria respectively. In contrast, they inhibited the growth of 70, 10, 20 and 0% Gram-negative respectively. All T. ferdinandiana extracts were either non-toxic (ethyl acetate, chloroform, hexane) with no significant increase in mortality induction, or of low toxicity (LC50 >1000 μg/ml) (methanol, deionised water) in the Artemia fransiscana bioassay. Conclusions: The low toxicity of the T. ferdinandiana extracts and their inhibitory bioactivity against bacteria validate Australian Aboriginal usage of T. ferdinandiana and indicates its medicinal potential as well as its potential as a source of natural ascorbic acid.