An Examination of the Antibacterial, Antifungal, Anti-Giardial and Anticancer Properties of Buchanania obovata Engl. Fruit Extracts

Background: Buchanania obovata is an endemic Australian plant that has been used traditionally to treat a variety of bacterial, fungal and protozoal pathogenic diseases. This study was undertaken to test B. obovata fruit extracts for the ability to inhibit microbial and cancer cell growth. Materials and Methods: B. obovata fruit powder was extracted and tested for antimicrobial activity using disc diffusion and MIC methods. Inhibitory activity against the gastrointestinal protozoal parasite Giardia duodenalis and antiproliferative activity against human colorectal (Caco2) and cervical (HeLa) cancer cell lines was evaluated using MTS-based colorimetric assays. Toxicity was evaluated using an Artemia franciscana nauplii bioassay. Results: The methanol, water and ethyl acetate B. obovata fruit extracts displayed potent antibacterial activity. The methanol and water extracts displayed the broadest specificity, inhibiting the growth of all of the Gram positive and Gram negative bacterial species tested. The ethyl acetate extract also displayed antibacterial activity, inhibiting the growth of 7 (88%) of the Gram negative and 2 (50%) of the Gram positive bacterial species. The methanol extract also displayed broad spectrum antifungal activity, inhibiting the growth of all 3 fungal species, including an ampicillin resistant strain of A. niger. The water extract also inhibited the growth of 2 (66%) of the fungal species tested. None of the extracts were particularly good inhibitors of the growth of the gastrointestinal parasite Giardia duodenalis. The methanolic and aqueous extracts were effective at blocking the proliferation of the colorectal cancer cell line Caco2 to between approximately 20 and 30% of the untreated cell growth. All extracts also inhibited HeLa cervical cancer cell growth. The methanol, water and ethyl acetate extracts displayed substantial toxicity in the Artemia nauplii assay. Conclusion: This study shows that B. obovata fruit extracts inhibit bacteria and fungi, but are relatively ineffective against G. duodenalis. The extracts were also effective inhibitors of Caco2 and HeLa cell proliferation, indicating that the extracts have potential in the treatment of microbial diseases and some cancers.