Interaction of Four Monoterpenes Contained in Essential Oils with Model Membranes:  Implications for Their Antibacterial Activity

Abstract

The present article reports the antimicrobial efficacy of four monoterpenes (thymol, carvacrol, p-cymene, and gamma-terpinene) against the Gram-positive bacterium Staphylococcus aureus and the Gram-negative bacterium Escherichia coli. For a better understanding of their mechanism of action, the damage caused by these four monoterpenes on biomembranes was evaluated by monitoring the release, following exposure to the compounds under study, of the water-soluble fluorescent marker carboxyfluorescein (CF) from large unilamellar vesicles (LUVs) with different lipidic composition (phosphatidylcholine, PC, phosphatidylcholine/phosphatidylserine, PC/PS, 9:1; phosphatidylcholine/stearylamine, PC/SA, 9:1). Furthermore, the interaction of these terpenes with dimyristoylphosphatidylcholine multilamellar vesicles as model membranes was monitored by means of differential scanning calorimetry (DSC) technique. Finally, the results were related also with the relative lipophilicity and water solubility of the compounds examined. We observed that thymol is considerably more toxic against S. aureus than the other three terpenes, while carvacrol and p-cymene are the most inhibitory against E. coli. Thymol and carvacrol, but not gamma-terpinene and p-cymene, caused a concentration-dependent CF leakage from all kinds of LUVs employed; in particular, thymol was more effective on PC and PC/SA LUVS than on PC/PS vesicles, while carvacrol challenge evoked a CF leakage from PC/PS LUVs similar to that induced from PC/SA LUVs, and lower than that measured with PC vesicles. Concerning DSC experiments, these four terpenes caused a decrease in Tm and (especially carvacrol and p-cymene) DeltaH values, very likely acting as substitutional impurities. Taken together, our findings lead us to speculate that the antimicrobial effect of thymol, carvacrol, p-cymene, and gamma-terpinene may result, partially at least, from a gross perturbation of the lipidic fraction of the plasmic membrane of the microorganism. In addition to being related to the physicochemical characteristics of the compounds (such as lipophilicity and water solubility), this effect seems to be dependent on the lipidic composition and net surface charge of the microbic membranes. Furthermore, the compounds might cross the cell membranes, thus penetrating into the interior of the cell and interacting with intracellular sites critical for antibacterial activity.

Chemical composition and antibacterial activity of essential oils ofLantana camara,Ageratum houstonianumandEupatorium adenophorum

“…Carvacrol, an important constituent of the essential oils of oregano and thyme stimulates E. coli O157:H7 to produce Hsp60 and prevents the synthesis of flagellin, causing cells to be aflagellate and therefore non-motile (Burt et al, 2007). The hydrophobicity of essential oils enables them to partition in the lipids of the cell membrane and mitochondria, rendering them permeable and leading to leakage of cell contents (Burt, 2004;Cristani et al, 2007).…”

Thymol and carvacrol: biotransformation and antifungal activity against the plant pathogenic fungi Colletotrichum acutatum and Botryodiplodia theobromae

“…The mode of action for (C) and (T) is uncertain; however, activity may be linked to the hydrophobicity and consequently, the ability of both compounds to pass through the fungal cell membrane (Knobloch et al, 1988), which further affects pH homeostasis and equilibrium of inorganic ions (Ultee et al, 2000;Cristani et al, 2007) disturbing the cell structures. Furthermore, the involvement of the hydroxyl group in the formation of hydrogen bonds and the acidity of these phenolic compounds may be another important factor involved in the bioactivity.…”

Synthesis, Antimicrobial Activity and in silico Studies on Thymol Esters

“…[11][12][13][14][15][16] The mode of action of thymol against yeast and fungi has been sparsely investigated, though certain studies point to interactions with the cell envelope and intracellular targets. [16][17][18][19] Thymyl derivatives are well represented in Asteraceae plants, particularly within tribes Senecioneae, Eupatorieae, Inuleae and Helenieae. In some Inula, Doronicum and Pulicaria species, thymyl derivatives rather than sesquiterpenoids are the major root constituents.…”

“…Keeping in view diverse pharmacological activities of thymol [7][8][9][10][11][12][13][14][15][16][17][18][19] and preliminary results on bioactivity of thymyl derivatives 4,5,22,25,[28][29][30]33 we have set the aim of our study. By making a single modification of a phenolic functionality in thymol we have obtained a series of ester compounds (3a-t), performed their structural characterization, in vitro antimicrobial testing and in silico calculation of physico-chemical, pharmacokinetic and toxicological properties.…”