Antibacterial activity and toxicity of Terminalia Ferdinandia (Kakadu Plum) fruit extract

Abstract

Introduction: Terminalia ferdinandiana (TF) is an endemic Australian native plant long used as a food and a medicinal agent by Indigenous Australians. Yet the medicinal bioactivities of this plant are poorly studied. Methods: TF extracts were prepared with various solvents, dried and then re-dissolved in water. Antibacterial activity of these TF preparations was determined by growth inhibition against a panel of pathogenic bacteria and fungi. Toxicity (LC50) was assessed by the Artemia franciscanna (brine shrimp) nauplii bioassay. 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 (93%). Individual MIC's were as low as 30 姯ml for some bacteria. The deionised water extract inhibited the growth of 11 of the 14 bacteria tested (79%). The ethyl acetate, chloroform and hexane extracts inhibited 21%, 29% and 14% respectively. TF methanolic extracts were equally effective against Gram-positive (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 bacteria respectively. All TF extracts were either non-toxic (ethyl acetate, chloroform, hexane) with no significant increase in mortality induction, or of low toxicity (LC50 >1000 姯ml) (methanol, deionised water) in the Artemia fransiscana bioassay. Conclusions: The low toxicity of the TF extracts and their inhibitory bioactivity against a range of bacteria validate traditional Aboriginal usage of the Kakadu plum and indicates its medicinal potential as well as its value as a rich source of natural vitamin C.