The Inhibitory Activity of Mischarytera lauteriana (F.M.Bailey) Leaf Extracts against a Panel of Bacterial Pathogens

Introduction: The development of multi-antibiotic resistant strains of bacteria has necessitated the search for new, effective antibacterial therapies. M. lauteriana was used by Australian Aborigines as a nutritious food. However, very little research has been published on this species and the antibacterial activity of M. lauteriana leaf extracts has not yet been reported. Methods: The ability of M. lauteriana leaf extracts to inhibit the growth of gram-negative and gram-positive bacterial species was investigated by disc diffusion and growth time course assays. The growth inhibitory activity was further quantified by MIC determination. Toxicity was determined using the Artemia franciscana nauplii bioassay. Results: The methanolic and aqueous M. lauteriana leaf extracts were good inhibitors of the growth of both gram-positive and gram-negative bacteria. The methanolic extract was a particularly good inhibitor of K. pneumoniae and B. cereus growth, with MIC values of 728 and 515μg/mL respectively. The aqueous extract was also a good inhibitor of these bacteria (MICs of 953 and 860μg/mL respectively). Whilst the M. lauteriana leaf extracts also inhibited the growth of P. mirabilis, S. aureus and S. pyogenes, the MIC values (in the range 1000-2000μg/mL) were indicative of moderate inhibitory activity. The M. lauteriana leaf extracts were further investigated by growth time course assays against K. pneumoniae and B. cereus. Interestingly, both extracts showed significant growth inhibition within 1h of exposure against both bacterial species. All extracts were determined to be nontoxic in the Artemia franciscana nauplii bioassay, indicating their safety for the treatment of gram-positive bacterial infections. Conclusion: The lack of toxicity of the M. lauteriana leaf extracts and their growth inhibitory bioactivity against multiple bacteria indicate their potential in the development of new antibiotic chemotherapies.