Antimicrobial Constituents and Synergism Effect of the Essential Oils from Cymbopogon citratus and Alpinia galanga

From the fresh leaf sheathes of lemongrass (Cymbopogon citratus) and rhizomes of galanga (Alpinia galanga) light yellow and colorless oils, respectively, were obtained by hydrodistillation and microwave assisted extraction (MAE) in yields of 0.24% and 0.03%, and 0.11% and trace (w/w), respectively. By GC/MS analysis, five major constituents were identified in lemongrass oil, E-citral, Z-citral, β-myrcene, selina-6-en-4-ol, and cis-ocimene, and five in galanga oil, 1,8-cineole, phenol 4-(2-propenyl)-acetate, dl-limonene, α-pinene, and α-terpineol. Three major components of the combined lemongrass and galanga oils (ratio 7:3, 1:1, 3:7) were 1,8-cineole (46.3%, 31.5%, 19.3%), E-citral (12.8%, 22.7%, 32.8%) and Z-citral (8.5%, 15.2%, 21.6%). The MICs of lemongrass and galanga oils were: against Staphylococcus aureus 0.5% and 4%, v/v, against Pseudomonas aeruginosa 40% and >40%,v/v, against Streptococcus bovis 0.25% and 0.5%, v/v, and against Candida albicans 0.25% and 0.5%, v/v. Citral (from lemongrass oil) gave greater potentiation than 1,8-cineole (from galanga oil). The combination profiles of galanga oil with lemongrass oil (volume ratios 3:7, 1:1, and 7:3) were tested against the four pathogenic microorganisms. Synergistic activity was best noted for only one ratio (volume ratio 3:7) as the Σfic< 1 against all tested microorganisms. The present investigation provides evidenc that the utilization of two essential oils in combination should be assessed for synergistic antimicrobial activity in order to reduce their minimum effective dose.