Getmore Rumbudzai Chikowe1, Lindiwe Nomathemba Mpala2, Ian Edwin Cock1*
1School of Natural Sciences, Nathan Campus, Griffith University, 170 Kessels Rd, Nathan, Brisbane, Queensland 4111, Australia.
2Environmental Futures Research Institute, Nathan Campus, Griffith University, 170 Kessels Rd, Nathan, Brisbane, Queensland 4111, Australia.
Published: May 2017
Type: Original Article
Introduction: Cinnamomum oliveri F. M. Bailey is a rain forest tree native to Australia. Decoctions, infusions and essential oils produced from the leaves were used traditionally to treat a variety of bacterial diseases. Despite this, C. oliveri leaf extractions have not been rigorously examined for antibacterial properties against many pathogens. Methods: The antimicrobial activity of C. oliveri leaf extractions was investigated by disc diffusion and growth time course assays against a panel of pathogenic bacteria. The growth inhibitory activity was quantified by MIC determination. Toxicity was determined using the Artemia franciscana nauplii bioassay. Results: C. oliveri leaf solvent extractions inhibited the growth of a wide range of bacterial species. Growth of both gram positive and gram negative bacteria was inhibited by the C. oliveri leaf extracts to approximately the same extent. The methanolic extracts were generally most potent growth inhibitors. The methanolic, aqueous and ethyl acetate C. oliveri leaf extracts were particularly potent inhibitors of P. mirabilis growth, with MIC values as low as 127 μg/mL (methanolic extract). A. coli, K. pneumoniae and B. cereus were also particularly susceptible to the methanolic, aqueous and ethyl acetate extracts, with MIC values generally substantially <1000 μg/ mL. The antibacterial activity of the methanolic C. oliveri leaf extract was further investigated by growth time course assays which showed significant growth inhibition in cultures of E. coli, K. pneumoniae and P. mirabilis within 1 h of exposure. All extracts were determined to be nontoxic in the Artemia franciscana nauplii bioassay, indicating their safety for internal use as well as for topical uses. Conclusions: The lack of toxicity of the C. oliveri leaf extracts and their growth inhibitory bioactivity against a panel of pathogenic bacteria partially validate the traditional usage of these species to treat bacterial diseases and indicate their potential in the development of antiseptic agents.
Key words: Lauraceae, Oliver’s Sassafras, Black Sassafras, Camphorwood, Cinnamon wood, Australian Plants, Antibacterial Activity, Medicinal Plants.