Thymol was first isolated by the German chemist Caspar Neumann in 1719. In 1853, the French chemist A. Lallemand named thymol and determined its empirical formula. Thymol was first synthesized by the Swedish chemist Oskar Widman in 1882.
An in vitro study found thymol and carvacrol to be highly effective in reducing the minimum inhibitory concentration of several antibiotics against zoonotic pathogens and food spoilage bacteria such as Salmonella typhimurium SGI 1 and Streptococcus pyogenes ermB. In vitro studies have found thymol to be useful as an antifungal against food spoilage and bovine mastitis. Thymol demonstrates in vitro post-antibacterial effect against the test strains E. coli and P. aeruginosa (gram negative), and Staphylococcus aureus and B. cereus (gram positive). This antibacterial activity is caused by inhibiting growth and lactate production, and by decreasing cellular glucose uptake.
Thyme essential oil is useful in preservation of food. The antibacterial properties of thymol, a major part of thyme essential oil, as well as other constituents, are in part associated with their lipophilic character, leading to accumulation in bacterial membranes and subsequent membrane-associated events, such as energy depletion.
The antifungal nature of thymol against some fungi that are pathogenic to plants is due to its ability to alter the hyphal morphology and cause hyphal aggregates, resulting in reduced hyphal diameters and lyses of the hyphal wall.
Thymol has been used in alcohol solutions and in dusting powders for the treatment of tinea or ringworm infections, and was used in the United States to treat hookworm infections. People of the Middle East continue to use za'atar, a delicacy made with large amounts of thyme, to reduce and eliminate internal parasites. It is also used as a preservative in halothane, an anaesthetic, and as an antiseptic in mouthwash. When used to reduce plaque and gingivitis, thymol has been found to be more effective when used in combination with chlorhexidine than when used purely by itself. Thymol is also the active antiseptic ingredient in some toothpastes, such as Johnson & Johnson's Euthymol. Thymol has been used to successfully control varroa mites and prevent fermentation and the growth of mold in bee colonies, methods developed by beekeeper R. O. B. Manley. Thymol is also used as a rapidly degrading, non-persisting pesticide. Thymol can also be used as a medical disinfectant and general purpose disinfectant.
Studies have shown that hydrocarbon monoterpenes and thymol in particular degrade rapidly (DT50 16 days in water, 5 days in soil) in the environment and are, thus, low risks because of rapid dissipation and low bound residues, supporting the use of thymol as a pesticide agent that offers a safe alternative to other more persistent chemical pesticides that can be dispersed in runoff and produce subsequent contamination.
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