Essential oils and their components are becoming increasingly popular as naturally occurring antimicrobial agents. In this work the chemical composition and the antimicrobial properties of Thymus essential oils and of their main components were determined. Three essential oils obtained from different species of Thymus growing wild in Sardinia and a commercial sample of Thymus capitatus oil were analysed. The essential oil components were identified by GC/MS analysis. The antimicrobial activity of the oils and components was determined against a panel of standard reference strains and multiple strains of food-derived spoilage and pathogenic bacteria, using a broth microdilution method. The GC/MS analysis showed that the major constituents of the oils were monoterpene hydrocarbons and phenolic monoterpenes, but the concentration of these compounds varied greatly among the oils examined. The results of the antimicrobial assay showed that essential oils extracted from Sardinian Thymus species have an antimicrobial activity comparable to the one observed in other thyme oils. It seems also confirmed that the antimicrobial properties of thyme essential oils are mainly related to their high phenolic content. Among the single compounds tested carvacrol and thymol turned out to be the most efficient against both reference strains and food-derived bacteria. The results of this study confirmed the possibility of using thyme essential oils or some of their components in food systems to prevent the growth of foodborne bacteria and extend the shelf-life of processed foods.

In‐vitro antimicrobial activity and chemical composition of Sardinian Thymus essential oils

Screening methods to determine antibacterial activity of natural products

Tea tree oil, or the essential oil of Melaleuca alternifolia, is becoming increasingly popular as a naturally occurring antimicrobial agent. The antimicrobial activity of eight components of tea tree oil was evaluated using disc diffusion and broth microdilution methods. Attempts were also made to overcome methodological problems encountered with testing compounds which have limited solubility in aqueous media. After assessing media with and without solubilizing agents, the disc diffusion method was used to determine the susceptibility of a range of micro-organisms to 1,8-cineole, 1-terpinen-4-ol, rho-cymene, linalool, alpha-terpinene, gamma-terpinene, alpha-terpineol and terpinolene. While the disc diffusion method lacked reproducibility, it was considered useful as a procedure for screening for antimicrobial activity. Terpinen-4-ol was active against all the test organisms while rho-cymene demonstrated no antimicrobial activity. Linalool and alpha-terpineol were active against all organisms with the exception of Pseudomonas aeruginosa. Minimum inhibitory and minimum cidal concentrations of each component against Candida albicans, Escherichia coli and Staphylococcus aureus were determined using a broth microdilution method. Modifications to this method overcame solubility and turbidity problems associated with the oil components and allowed the antimicrobial activity of each of the components to be quantified reproducibly. There was reasonable agreement between minimum inhibitory concentrations and zones of inhibition. These results may have significant implications for the future development of tea tree oil as an antimicrobial agent.

Antimicrobial activity of the major components of the essential oil of Melaleuca alternifolia

Correlation between chemical composition and antibacterial activity of essential oils of some aromatic medicinal plants growing in the Democratic Republic of Congo.

Pharmacokinetics and metabolism of delta 1-tetrahydrocannabinol and other cannabinoids with emphasis on man.

Antibacterial constituents in the essential oil of Cymbopogon citratus (DC.) Stapf.

Chemical constituents of Cnestis ferruginea DC. I. Petroleum ether fraction

Preliminary phytochemical studies of Combretodendron macrocarpum (P. Beauv) Keay with reference to its hypotensive principles.

Six acidic metabolites were isolated from rat faeces and identified by gas chromatography-mass spectrometry and proton magnetic resonance. Cannabinol-7-oic acid was the most abundant acidic metabolite isolated. Others present in decreasing order of prominence were 1″-hydroxy-, 4”-hydroxy-, 3″-hydroxycannabinol-7-oic acid, cannabinol-3”-one-7-oic acid and 2″-hydroxycannabinol-7-oic acid.

Wolde-Ab Yisak

Papers

Antibacterial constituents in the essential oil of Cymbopogon citratus (DC.) Stapf.

Chemical constituents of Cnestis ferruginea DC. I. Petroleum ether fraction

Preliminary phytochemical studies of Combretodendron macrocarpum (P. Beauv) Keay with reference to its hypotensive principles.

Acidic in vivo metabolites of cannabinol isolated from rat faeces.