Mitchell Henry Wright,a Megan Sarah Jean Arnold,b Cameron Jay Lee,a Reece Courtney,a,c Anthony Carlson Greene,a Ian Edwin Cock,a,c*
aSchool of Natural Sciences, Nathan Campus, Griffith University, 170 Kessels Rd, Nathan, Queensland 4111, AUSTRALIA.
bEskitis Institute for Drug Discovery, Griffith University, Queensland, Australia, 46 Don Young Rd, Nathan, Queensland 4111, AUSTRALIA.
cEnvironmental Futures Research Institute, Nathan Campus, Griffith University, 170 Kessels Rd, Nathan, Queensland 4111, AUSTRALIA.
Published: January 2016
Type: Original Article
Introduction: Streptococcus pyogenes is a gram-positive, pathogenic bacterium which causes a variety of diseases including streptococcal pharyngitis, impetigo and rheumatic heart disease, depending on which tissue it infects. Many Terminalia spp. have documented therapeutic properties as general antiseptics, inhibiting the growth of a wide variety of bacterial species. Methods: Solvent extracts were prepared using Indian Terminalia spp. with documented ethnobotanical usage to treat bacterial infections, or published antibacterial activity. The extracts were investigated by disc diffusion assay for the ability to inhibit the growth of a clinical strain of S. pyogenes. Their MIC values were determined to quantify and compare their efficacies. Toxicity was determined using the Artemia franciscana nauplii bioassay. Results: T. arjuna, T. catappa and T. chebula methanolic and ethyl acetate extracts displayed potent antibacterial activity in the disc diffusion assay against S. pyogenes. The T. catappa and T. chebula ethyl acetate extracts were particularly potent, with MIC values of 225 and 205 μg/mL respectively. All methanolic extracts were also potent growth inhibitors with MIC values of 268 μg/mL (T. arjuna methanolic extract), 425 μg/mL (T. catappa methanolic extract) and 300 μg/mL (T. chebula methanolic extract). The T. catappa hexane extract was also a potent S. pyogenes growth inhibitor (MIC 768 μg/mL). All other extracts were either ineffective or were of only low efficacy. Furthermore, all of the Indian Terminalia spp. extracts were nontoxic in the Artemia fransiscana bioassay, with LC50 values >1000 μg/mL. Conclusion: The potent growth inhibitory bioactivity of the methanolic and ethyl acetate T. arjuna, T. catappa and T. chebula extracts against S. pyogenes demonstrates their potential for the treatment and prevention of pharyngitis, impetigo and rheumatic heart disease. All extracts were nontoxic indicating their safety for therapeutic use.
Key words: Terminalia arjuna, Terminalia catappa,Terminalia chebula pharyngitis, Impetigo, Rheumatic heart disease, Antibacterial activity, Ayurveda.