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

The present article reports the antimicrobial efficacy of four monoterpenes (thymol, carvacrol, p-cymene, and γ-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 c...

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Bibliographic Details
Published in:Journal of agricultural and food chemistry 2007-07, Vol.55 (15), p.6300-6308
Main Authors: Cristani, Mariateresa, D'Arrigo, Manuela, Mandalari, Giuseppina, Castelli, Francesco, Sarpietro, Maria Grazia, Micieli, Dorotea, Venuti, Vincenza, Bisignano, Giuseppe, Saija, Antonella, Trombetta, Domenico
Format: Article
Language:English
Subjects:
Anti-Bacterial Agents - pharmacology
antimicrobial properties
Aroma and flavouring agent industries
Biological and medical sciences
carvacrol
cell membranes
cytotoxicity
Escherichia coli
Escherichia coli - drug effects
essential oils
Food industries
Food microbiology
Fundamental and applied biological sciences. Psychology
gamma-terpinene
in vitro studies
mechanism of action
membrane permeability
Monoterpenes - analysis
Monoterpenes - chemistry
Monoterpenes - pharmacology
monoterpenoids
Oils, Volatile - chemistry
p-cymene
phosphatidylcholines
phosphatidylserines
phospholipids
plasma membrane
species differences
Staphylococcus aureus
Staphylococcus aureus - drug effects
stearylamine
thymol
Thymol - pharmacology
Unilamellar Liposomes - chemistry
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Summary:The present article reports the antimicrobial efficacy of four monoterpenes (thymol, carvacrol, p-cymene, and γ-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 γ-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 T m and (especially carvacrol and p-cymene) ΔH 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 γ-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. Keywords: Thymol; carvacrol; p-cymene; γ-terpinene; Staphylococcus aureus; Escheric
ISSN:0021-8561
1520-5118
DOI:10.1021/jf070094x