Abstract: The essential oil of Plectranthus tomentosa was extracted by steam distillation and was analyzed using gas chromatography-mass spectroscopy (GC-MS). Thirty-one compounds accounting for 92.94% of the total oil were identified by area normalization method.The main constituents were Aliphatic olefins,alcohols,esters,alkanes,aromatic hydrocarbons compounds.Limonene was found to be the most abundant component (36.86%) of P.tomentosa oil. The essential oil had obvious antibacterial effect according to experiments.Then,minimal inhibitory concentration (MIC) and minimum bactericidal concentration (MBC) were detected against four bacteria strains by Plate Counting method.The results showed that the essential oil had no inhibition on Enterobacter sakazakii, but had a strong inhibitory effect on Escherichia coli, Staphylococcus aureus and Salmonella typhi. The inhibitory effect on S.aureus was the strongest,MIC and MBC were 1 μL/mL and 5 μL/mL respectively.

Key words: Plectranthus tomentosa, essential oil, chemical composition, antimicrobial activity, analysis