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The specie Lippia gracilis Schauer is largely utilized for their antimicrobial properties, which are attributed to the presence of phenolic monoterpenes such as thymol and carvacrol. The aim of this study was to determine the yields and chemical composition of the essential oils obtained from fresh and dry leaves of collected at different times in the city of Crato-CE, in January 2009. The essential oils were extracted by hydrodistillation, and its components were identified by gas chromatography coupled with mass spectrophotometry. The time of plant collection should coincide with the moment of greatest expression of the active principle.

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Abstract:The chemical composition of the essential oil obtained from the fresh and dried leaves of Lippia gracillis Schauer, Verbenaceae, was analyzed by gas chromatography and gas chromatography/mass spectrometry (GC⁄MS). The yield of essential oil extracted from the dried leaves was significantly higher (p<0.05) when compared to the fresh leaves. Seventeen components were identified. The monoterpenes and sesquiterpene hydrocarbons with 96.26% (w/w) of the total oil obtained of fresh leaves and 86.99% (w/w) of the total oil obtained of dried leaves were the principal compound groups. Thymol was observed dominant (44.42%; 21.3%), followed by carvacrol (22.21%; 21.30%), p-cymene (6.23%; 8.58%), α-pinene (5.65%; 19.42%), β-caryophyllene (5.61%; 3.57%) and other minor constitutes, respectively. Microbiological results obtained by agar diffusion method, micro dilution method and minimum inhibitory concentration (MIC) showed that the essential oil has a relevant antimicrobial activity against E. coli (ATCC 10536), E. coli (Ec 27), Pseudomonas aeruginosa (ATCC 15442), S. aureus (ATCC 12692) and S. aureus (Sa 358), with their inhibition zones ranging from 9 to 13 mm and the MIC ranging from 64 to 512 μg/mL.

Lippia gracilis Schauer (Verbenaceae) is an aromatic plant widely used in folk medicine in the Brazilian semi-arid region. This work aims at evaluating the anti-microbial activity of essential oils from the leaves of L. gracilis (EOLG) when associated with commercial antibiotics against bacterial resistance. The essential oil obtained by hydrodistillation has 38 chemical constituents with thymol (44.4%), carvacrol (22.2%), p-cymene (6.2%) and α-pinene (5.6%) as major constituents. Microbiological assays were conducted by direct and gaseous contacts. We demonstrated that EOLG has significant synergism with all antibiotics tested. EOLG decreased the minimal inhibitory concentration of the aminoglycosides and improved their zone of inhibition more than 300% against Staphylococcus aureus and 270% against Pseudomonas aeruginosa. These results demonstrate that natural substances present in EOLG have the capacity to modulate bacterial resistance and can be used as an adjuvant therapy against multi-resistant microorganisms such as S. aureus, Escherichia coli and P. aeruginosa.

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