Chemical and Biological Characterization of Novel Essential Oils from 'Eremophila bignoniiflora' (F. Muell) (Myoporaceae): A Traditional Aboriginal Australian Bush Medicine

Abstract

Essential oils were extracted by hydrodistillation from the traditional Australian medicinal plant 'Eremophila bignoniiflora', characterized chemically and then screened for bioactivity. Characterization and quantification were completed using gas chromatography-mass spectrometry (GC-MS) and GC-flame ionization detection, respectively. Antimicrobial capacity was assessed using disc diffusion and micro-titre plate broth dilution and further characterized using thin layer chromatography followed by bioautography to assign activity to separated individual active components. Antifungal capacity was investigated using micro-titre plate broth dilution against pathogenic Trichophyton species. Free radical scavenging ability was assessed using the diphenylpicrylhydradyl reaction in methanol. The predominant components of the essential oil were fenchyl-acetate and bornyl-acetate. However, bioautography indicated antimicrobial ability to be largely linked to the less abundant, more polar constituents. Oils displayed only modest antifungal ability against pathogenic Trichophyton species associated with dermatophytosis, but moderate to high antimicrobial activity, particularly against the yeast Candida albicans and the bacteria 'Staphylococcus epidermidis'. Essential oils exhibited relatively low free radical scavenging ability. Speculation over the role of essential oils in the traditional medicinal applications of 'E. bignoniiflora' follows, exploring correlations between traditional use and investigated bioactivities.