Determination of essential oils and components for increasing effectiveness of antimicrobial substances

In the frame of this project, six clinical and standard pathogenic drug resistant strains, namely; Gram (+) Staphylococcus aureus, Gram (-) Escherichia coli and antifungal susseptible Candida albicans were used as in vitro antimicrobial targets using the modified CLSI (Clinical Laboratory Standards Institute) microdilution method. European Pharmacopoiea grade Matricaria recutita L., Lavandula latifolia Medik., Pinus mugo Turra, Citrus reticulata Blanco. essential oils (Aetheroleum) were used as natural antimicrobials. Essential oil fractions by column chromtography using n-hexane, diethyl ether, dichloromethane and methanol, respectively were used to increase the antimicrobial activity. Addiditonally, some components such as R-(+)-limonene, (+)-linalool, 1,8-cineole, (±)- camphor, β-caryophyllene, α-pinene, (-)-β-pinene, γ-terpinene, farnasene, bisabolool and (+)-δ-3-carene were used. The standard antimicobials ampicillin, sefuroxime, tetracycline, fluconazole, nystatin were combined with the essential oils or derived test materials using the Checkerboard method. The minimum inhibitory concentrations (MIC) were determined using the microdilution method, fractional inhibitory concentrations (FIC) of the combinations were classified as synergistic, additive, indifferent, and antagonistic, respectively, for all the tested materials against the microorganisms. In addition, the active combinations were subjected to in vitro WS1-XTT cytotoxicity (human skin fibroblasts) and bioluminescent Aliivibrio fischeri NRRL B 11177 toxicity assays to determine the selectivity profile comparatively. As a conclusion, this is the first report on the synergistic/additive activity of the desinged essential oil combinations. Overall, 54 sinergistic, 75 additive, and 108 indifferent activity results towards the efficacy were observed, where the toxicity was lowever. Key words: Antibiotic resistant bacteria, Candida albicans, Essential Oils, Combination studies, Checkerboard method, Synergistic effect.