GC-MS analysis of bioactive Petalostigma extracts: Toxicity, antibacterial and antiviral activities.

Abstract

ABSTRACT Introduction: Petalostigma (known locally as quinine tree), an Australian genus of the Euphorbiaceae family, has a long history of ethnopharmacological usage in the treatment of sore eyes and toothaches, as well as usage as a general antiseptic agent. Methods: P. pubescens, and P. triloculare solvent extracts were tested for antimicrobial activity, antiviral activity and toxicity in vitro by disc diffusion assays, MS2 bacteriophage plaque reduction assays and Artemia nauplii mortality bioassays respectively. Results: The methanol, water and ethyl acetate leaf and fruit extracts of P. pubescens, and P. triloculare displayed potent antibacterial activity in the disc diffusion assay. The methanol and ethyl acetate extracts proved to have the broadest specificity, inhibiting the growth of 10 of the 14 bacteria tested (71 %) for the leaf extract and 9 of the 14 bacteria tested (64 %) for the fruit extracts. The water extracts of the leaf and fruit also had broad spectrum antibacterial activity, inhibiting the growth of 8 (57 %) and 7 (50 %) of the 14 bacteria tested respectively. All extracts which displayed antibacterial activity were approximately equally effective against Gram-positive and Gram-negative bacteria, each inhibiting the growth of 50-75% of the Gram-positive and Gram-negative bacteria tested. The methanol, water and ethyl acetate extracts also displayed antiviral activity in the MS2 plaque reduction assay. The methanol and water extracts inhibited 26.6 - 49.0 % and 85.4 - 97.2 % of MS2 plaque formation respectively, with the fruit extracts being more potent inhibitors. All ethyl acetate extracts inhibited 100 % of MS2 plaque formation. All P. pubescens, and P. triloculare extracts were also shown to be non-toxic or of low toxicity in the Artemia fransiscana bioassay. Analysis of these extracts by RP-HPLC showed that the P. triloculare ethyl acetate fruit extract was the least complex of the bioactive extracts. Subsequent analysis of this extract by GC-MS revealed that it contained 9 main compounds: acetic acid; 2,2-dimethoxybutane; 4-methyl-1,3-dioxane; decane; unadecane; 2-furanmethanol; 1,2-benzenediol; 1,2,3-benzenetriol; and benzoic acid. Conclusions: The lack of toxicity of the P. pubescens, and P. triloculare extracts and their inhibitory bioactivity against bacteria and viruses validate Australian Aboriginal usage of Petalostigma species and indicates its medicinal potential.