Chemical composition and antimicrobial activity of a newly identified chemotype of Achillea wilhelmsii K.Koch from Kashan, Iran

Achillea wilhelmsii K.Koch (Asteraceae) is traditionally used in Kashan (Iran) to control diabetes, headaches, kidney stones and heartburn. Due to its beneficial properties, the aerial parts of the plant were collected from the area of Maragheh (Kashan, Isfahan, Iran), in June 2022, during its full flowering, and the essential oil was obtained by hydrodistillation (Clevenger). The yield, composition and antimicrobial activity of the extractive solution were measured. Qualitative evaluation was performed by means of gas chromatography-mass spectroscopy method, and antimicrobial activity was determined against 12 strains of microorganisms by measuring inhibition halo, minimum inhibitory concentration, and minimum bactericidal concentration (MBC). The yield of essential oil was ~ 0.1071% (w/w) and it mainly contained oxygenated monoterpenes (47.87%), being for the first time fragranol (33.22%), fragranyl acetate (16.18%) and oleic acid (6.33%) the most abundant. The highest inhibitory halo was found against Candida albicans and Gram-positive Staphylococcus aureus (~ 10 mm). The essential oil was also effective against gram-negative bacteria such as Acinetobacter baumannii and Shigella dysenteriae, as the inhibition halo was ~ 9 mm and similar to that of rifampin, used as a reference. Therefore, it seems that this essential oil from and endemic species has a unique chemotype with potential antimicrobial activity, which may be a possible option for fragranol isolation and the production of natural antibiotics effective against various microorganisms.