Antibacterial Activity, Antioxidant Potential and Stigmasterol Isolation from Laggera aurita Linn (Asteraceae)

Abstract

The study was aimed at the in-vitro investigation of the antibacterial activity, antioxidant potential and bioactive compound isolation from ethyl acetate crude fraction of Laggera aurita (L. aurita) Linn. The crude fraction was tested against five gram negative bacteria (Escherichia coli, Pseudomonas aeruginosa, Klebsiella pneumoniae, Salmonella typhi, Proteus mirabilis) and three gram positive bacteria (Staphylococcus aureus, Enterococcus faecalis and Bacillus subtilis) using macro dilution technique. The antioxidant potentials were evaluated using two different but complementary methods namely ferrous ion chelating activity (FICA) and ferric reducing antioxidant potential (FRAP). Phytocompound isolation was carried out on low pressure open column chromatography. The crude fraction displayed moderate to significant activity against all tested bacteria exhibiting both bacteriostatic and bactericidal effects. The crude fraction showed Minimum Inhibitory Concentration (MIC) and Minimum Bactericidal Concentration (MBC) in the range of 62.50-250 µg/mL and 125-1000 µg/mL respectively. The crude fraction was bactericidal to all tested pathogens except E. coli. The fifty percent effective concentration (EC50) of EDTA standard and the ethyl acetate fraction were obtained as 10.87 μg/mL and 25.77 μg/mL respectively. Similarly the FRAP determinations for ascorbic acid and ethyl acetate fraction yielded 153.63 and 134.40 Fe2+ Equivalent per g of fraction indicating 80.06% and 70.61% FRAP units respectively. The isolated phytocompound coded LAE was obtained as a white crystalline solid with melting point of 136‐138°C and Rf of 0.56 in hexane: ethylacetate (6:4). The isolated compound was identified by spectroscopic data analysis from FT-IR, GC-MS, 1D and 2D NMR and in comparison with literature. The compound was identified as stigmasterol. The observed significant antibacterial and antioxidant properties demonstrated by L. aurita in this study validate its widespread use in traditional medicine. Therefore the study had shown that L. aurita contains bioactive principles and may serve as a source for potential antibacterial and oxidative stress therapeutic agents.