The aim of the study was to characterise the chemical composition of the essential oil extracted from a Chinese traditional aromatic herb, Artemisia sieversiana Ehrhart ex Willd and investigate its antimicrobial activities against Staphylococcus aureus, the test bacterium, using thin-layer chromatography-direct bioautography (TLC-DB). Gas chromatography-mass spectrometry analysis showed that the essential oil was dominated by chamazulene (44.44%). Undeveloped TLC-DB enabled the measurement of zone of inhibition as valid as and more sensitive than the traditional agar diffusion method. The overall antimicrobial effect was weak at the tested concentration range and the antimicrobial strength did not exhibit concentration dependence. At high essential oil concentration (>1000μg/ml), size of zone of inhibition was all <7mm. Developed TLC-DB separated the components and visualised the inhibition of bacterial growth on the plate surface where the active antimicrobials were determined to be the minor components, hydroxylated terpenes, rather than the dominant component, chamazulene.
Keywords: Essential oil; antimicrobial activity; chamazulene; thin-layer chromatography-direct bioautography.