An examination of the medicinal potential of Scaevola spinescens: Toxicity, antibacterial, and antiviral activities

Abstract

Introduction: S. spinescens is an endemic Australian native plant with a history of use as a medicinal agent by indigenous Australians. Yet the medicinal bioactivities of this plant are poorly studied. S. spinescens solvent extracts were tested for antimicrobial activity, antiviral activity and toxicity in vitro. Results: All extracts displayed antibacterial activity in the disc diffusion assay. The methanol extract proved to have the broadest specificity, inhibiting the growth of 7 of the 14 bacteria tested (50 %). The water, ethyl acetate, chloroform and hexane extracts inhibited the growth of 6 (42.9 %), 5 (35.7 %), 5 (35.7 %), and 4 (28.6 %) of the 14 bacteria tested respectively. S. spinescens methanolic extracts were equally effective against Gram-positive (50 %) and Gram-negative bacteria (50 %). All other extracts were more effective at inhibiting the growth of Gram-negative bacteria. All extracts also displayed antiviral activity in the MS2 plaque reduction assay with the methanol, water, ethyl acetate, chloroform and hexane extracts inhibiting 95.2 ᠱ.8 %, 72.3 ᠶ.3 %, 82.6 ᠴ.5 %, 100 ᠰ % and 47.7 ᠱ2.9 % of plaque formation respectively. All S. spinescens extracts were non-toxic in the Artemia fransiscana bioassay with no significant increase in mortality induced by any extract at 24 and 48 h. The only increase in mortality was seen for the water extract at 72h, although even this extract displayed low toxicity, inducing only 41.7 ᠲ3.3 % mortality. Conclusions: The lack of toxicity of the S. spinescens extracts and their inhibitory bioactivity against bacteria and viruses validate Australian Aboriginal usage of S. spinescens and indicates its medicinal potential.