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.

The First Australians had well-developed healing systems. Groote Eylandt inhabitants used a variety of plant species to treat diarrhoea and other gastrointestinal illnesses. This study was undertaken to test, identify, and evaluate traditional medicines to treat these conditions against gastrointestinal bacterial, protozoal, and viral pathogens, as well as against cancer cell proliferation. Six plant species (Buchanania obovata Engl., Casuarina equisetifolia L., Eucalyptus tetrodonta F. Muell., Planchonia careya (F. Muell.) R. Knuth, Terminalia carpentariae C. T. White, and Vigna vexillata (L.) A. Rich.) were selected from a survey of a panel of elders from the Warnindhilyagwa tribe and compared with the published literature. Decoctions prepared according to traditional methods were screened for growth inhibitory activity of a panel of diarrhoea-causing bacterial pathogens by disc diffusion and liquid dilution MIC assays. Inhibitory activity against the gastrointestinal protozoal parasite Giardia duodenalis and antiproliferative activity against human colorectal (Caco2) and cervical (HeLa) cancer cell lines were evaluated using MTS-based colorimetric cell proliferation assays. Preliminary antiviral screening was accomplished using an MS2 bacteriophage plaque reduction assay. Toxicity was evaluated using Artemia franciscana nauplii mortality and HDF cell viability bioassays. All traditional medicines tested inhibited bacterial growth, often with MIC values substantially <1000 μg/mL. T. carpentariae was particularly noteworthy, with MIC values of 230–350 μg/mL against Citrobacter freundii, Salmonella newport, Shigella sonnei, Staphylococcus aureus, and Staphylococcus epidermidis. This species also had MICs 450–950 μg/mL against all other bacterial pathogens. B. obovata Engl. and E. tetrodonta were also good inhibitors of bacterial growth, albeit with substantially higher MIC values than determined for T. carpentariae. The T. carpentariae decoction was also the best inhibitor of MS2 phage replication (IC50 = 427 μg/mL) and Caco2 and HeLa proliferation (IC50 values of 885 and 85 μg/mL, respectively). None of the extracts were particularly strong inhibitors of Giardia duodenalis growth. All decoctions were nontoxic in the Artemia nauplii and HDF cell viability bioassays, indicating their suitability for therapeutic use.