Lindiwe Nomathemba Mpala1, Getmore Rumbudzai Chikowe1, Ian Edwin Cock1,2,*
1Environmental Futures Research Institute, Griffith University, 170 Kessels Rd, Nathan, Brisbane, Queensland 4111, Australia.
2School of Natural Sciences, Nathan Campus, Griffith University, 170 Kessels Rd, Nathan, Brisbane, Queensland 4111, Australia.
Published: October 2018
Type: Original Article
Introduction: Alpinia caerulea is a perennial herb which grows in coastal regions of Australia. All parts of this species are consumed as a bushfood. Furthermore, A. caerulea is taxonomically related to several plant species with well documented antimicrobial properties. Despite this, A. caerulea leaf solvent extractions have not previously been examined for antibacterial properties. Methods: The antimicrobial activity of A. caerulea leaf solvent 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: Methanolic and aqueous A. caerulea leaf extracts inhibited the growth of a range of gram positive and gram negative bacterial species. The methanolic extract was generally a more potent growth inhibitor than the aqueous extract. The methanolic and aqueous extracts were particularly potent inhibitors of S. marcenscens growth, with MIC values as low as 188 μg/mL for the methanolic extract. P. mirabilis (MICs of 785 and 976 μg/mL for the methanolic and aqueous extracts respectively) and K. pneumoniae growth (MICs of 1167 and 924 μg/mL for the methanolic and aqueous extracts respectively) were also particularly susceptible to the A. caerulea leaf extracts. The antibacterial activity of the methanolic and aqueous A. caerulea leaf extracts was further investigated by growth time course assays which showed significant growth inhibition in cultures of S. marcenscens 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. Conclusion: The lack of toxicity of the A. caerulea leaf extracts and their growth inhibitory bioactivity against a panel of pathogenic bacteria indicate their potential in the development of antibiotic agents.
Key words: Alpinia caerulea, Zingiberaceae, Native ginger, Blue berry ginger, Rheumatoid arthritis, Ankylosing spondylitis, Antibacterial activity, Medicinal plants.