A Comparative Evaluation of the Antimicrobial Activities of the Essential Oils of Three Salvia Species Growing in Egypt, Obtained by Hydrodistillation and Microwave-Assisted Hydro-distillation

Abstract

Since ancient times, the three Salvia L. species: Salvia aegyptiaca L., Salvia lanigera Poir., and Salvia multicaulis Vahl, have been utilised in traditional medicine all across the world. These species are now subjected to in-depth chemical and pharmacological investigations in order to find physiologically active chemicals. In the present study, the essential oil composition and biological activity of these Salvia L. species were studied. Using various extraction methods: hydrodistillation (HD) and microwave-assisted hydrodistillation (MAHD) to compare extraction efficiency, volatile metabolites were analysed and characterised by Gas chromatography/mass spectroscopy (GC/MS), while the antimicrobial efficiency for both the HD and MAHD essential oils was examined against four pathogens: Staphylococcus aureus, Escherichia coli, Aspergillus niger, and Candida albicans using microdilution assay. S. aegyptiaca, 12 and 14 compounds, were characterised by HD and MAHD extraction, respectively. Sesquiterpene hydrocarbons (85.87% HD & 72.74% MAHD) repidentified by HD and MAHD extraction, respectively. Monoterpenes (36.58% HD and 49.63% MAHD) and their oxygenated derivatives (31.4% HD and 28.63% MAHD) were the predominant compound classes. From S. lanigera, 12 and 8 compounds were identified by HD and MAHD extraction, respectively. Sesquiterpene hydrocarbons were present in S. lanigera essential oils with 8.3% HD and 2.4% MAHD. Moreover, the most potent antimicrobial activity was observed with the S. multicaulis essential oil collection employing either HD or MAHD extraction, while S. lanigera essential oils extracted by MAHD exhibited almost as high antimicrobial activity. The approach of MAHD saves time with all the improvements in product yield. Essential oils extracted using MAHD might be used to treat bacterial infections instead of standard antibacterial medications.