Chemical constituents and in vitro antimicrobial activity of rhizome essential oils of Zingiber densissimum SQTong & YMXia and Kaempferia laotica Gagnep. growing wild in Vietnam

Zingiber densissimum S.Q.Tong & Y.M.Xia and Kaempferia laotica Gagnep., belong to the Zingiberaceae family, which were found in Vietnam and Laos in recent years. To date, there has been very limited information on their phytochemical profiles and pharmacological activities. The present study was conducted to give insights into the chemical composition of the essential oils isolated from two plants and their antimicrobial activities. Gas Chromatographic-Mass Spectral (GC-MS) analysis was utilized to identify the chemical composition of the rhizome essential oils of Z. densissimum and K. laotica. The antimicrobial activities were evaluated on three Gram-positive bacterial strains, three Gram-negative bacterial strains, and a pathogenic yeast. The GC-MS analysis showed that beta-pinene (38.36%), beta-phellandrene (26.85%), and alpha-pinene (13.31%) were the most dominant components in Z. densissimum rhizome essential oil, while K. laotica rhizome essential oil was found to contain mainly camphene (23.44%), alpha-pinene (10.69%), 3-carene (8.60%) and beta-pinene (6.85%). As for the antimicrobial activity test results, the rhizome essential oil of Z. densissimum displayed potent activities against Candida albicans (MIC value = 2 mu g/mL), Enterococcus faecalis, Staphylococcus aureus, and Escherichia coli (MIC values = 8 mu g/ mL). Meanwhile, the rhizome essential oil of K. laotica showed weaker activities against all investigated microbial strains (MIC values ranging from 32 to 256 mu g/mL). The study results indicated the chemical constituents of the essential oils prepared from these plants. The two essential oil samples were also shown to exhibit potential antimicrobial activities against several pathogenic bacterial and fungal strains.