Chemical Compositions and Antibacterial Activity of Essential Oils from the Leaves and Rhizomes of Amomum unifolium Gagnep. from Vietnam

Plant essential oils have been used for hundreds of years as natural medicines to combat a multitude of pathogens, including bacteria, fungi, and viruses. The paper reports the chemical compositions of essential oil hydrodistilled from the leaves and rhizomes of Amomum unifolium Gagnep. from Vietnam. The main classes of compounds present in the essential oils were monoterpene hydrocarbons (10.1% and 23.9%, respectively), oxygenated monoterpenes (14.5% and 4.9%, respectively), sesquiterpene hydrocarbons (40.9% and 21.9%, respectively), and oxygenated sesquiterpenes (20.1% and 26.8%, respectively). Diterpenes (16.1%) were identified in sizeable proportion in the rhizome essential oil. The constituents occurring in higher amounts in the leaf essential oil were aromadendrene (6.9%), occidenol (6.8%), beta-phellandrene (6.2%), beta-elemene (5.7%), and delta-elemene (5.0%). However, the main compounds of the rhizome essential oil were beta-phellandrene (18.5%), torulosol (16.1%), germacrene D (5.7%), alpha-cadinol (5.5%) and (6S, 7R)-bisabolene (5.1%). The leaf essential oil of A. unifolium displayed higher antibacterial activity than the rhizome oil. The leaf oil showed activity towards S. aureus ATCC 6538, and B. pumilus ATCC 14884, with MIC values of 75.0 mu g/mL and 37.5 mu g/mL, respectively. On the other hand, the rhizome essential oil displayed activity against the organisms at MIC value of 150.0 mu g/mL. Both essential oils exhibited antibacterial activity to E. coli ATCC 8739, with MIC value of 150.0 mu g/mL. The antimicrobial activity of A. unifolium essential oils are being reported for the first time as a confirmation of the ethnomedical uses of A. unifolium in the treatment of diseases especially antimicrobial infections. Furthermore, the paper discusses the chemotaxonomy of Amomum oil samples.