title: Mechanisms of antibacterial action of three monoterpenes.
abstract: In the present paper, we report the antimicrobial efficacy of three monoterpenes [linalyl acetate, (+)menthol, and thymol] against the gram-positive bacterium Staphylococcus aureus and the gram-negative bacterium Escherichia coli. For a better understanding of their mechanisms of action, the capability of these three monoterpenes to damage biomembranes was evaluated by monitoring the release, following exposure to the compounds under study, of the water-soluble fluorescent marker carboxyfluorescein from unilamellar vesicles with different lipidic compositions (phosphatidylcholine, phosphatidylcholine/phosphatidylserine [9:1], phosphatidylcholine/stearylamine [9:1], and phosphatidylglycerol/cardiolipin [9:1]). Furthermore, the interaction of the terpenes tested with dimyristoylphosphatidylcholine multilamellar vesicles as model membranes was monitored by means of differential scanning calorimetry. Finally, the results were related to the relative lipophilicity and water solubility of the compounds examined. Taken together, our findings lead us to speculate that the antimicrobial effect of (+)menthol, thymol, and linalyl acetate may result, at least partially, from a perturbation of the lipid fraction of microorganism plasma membrane, resulting in alterations of membrane permeability and in leakage of intracellular materials. Besides being related to physicochemical characteristics of the drugs (such as lipophilicity and water solubility), this effect seems to be dependent on lipid composition and net surface charge of microbial membranes. Furthermore, the drugs might cross the cell membranes, penetrating into the interior of the cell and interacting with intracellular sites critical for antibacterial activity.
authors.affiliation: Department Farmaco-Biologico, School of Pharmacy, University of Messina, Contrada Annunziata, 98168 Messina, Italy.
authors.forename: Domenico
authors.initials: D
authors.lastname: Trombetta
authors.forename: Francesco
authors.initials: F
authors.lastname: Castelli
authors.forename: Maria Grazia
authors.initials: MG
authors.lastname: Sarpietro
authors.forename: Vincenza
authors.initials: V
authors.lastname: Venuti
authors.forename: Mariateresa
authors.initials: M
authors.lastname: Cristani
authors.forename: Claudia
authors.initials: C
authors.lastname: Daniele
authors.forename: Antonella
authors.initials: A
authors.lastname: Saija
authors.forename: Gabriela
authors.initials: G
authors.lastname: Mazzanti
authors.forename: Giuseppe
authors.initials: G
authors.lastname: Bisignano
mesh_terms: D000900:Anti-Bacterial Agents / Q000494:pharmacology*; D002152:Calorimetry, Differential Scanning; D002462:Cell Membrane / Q000737:chemistry / Q000187:drug effects; D002463:Cell Membrane Permeability / Q000187:drug effects; D004926:Escherichia coli / Q000187:drug effects*; D005452:Fluoresceins / Q000378:metabolism; D008055:Lipids / Q000032:analysis; D008081:Liposomes / Q000737:chemistry; D008610:Menthol / Q000494:pharmacology; D008826:Microbial Sensitivity Tests; D039821:Monoterpenes / Q000494:pharmacology*; D013211:Staphylococcus aureus / Q000187:drug effects*; D013943:Thymol / Q000494:pharmacology
chemical_list: D000900:Anti-Bacterial Agents; D005452:Fluoresceins; D008055:Lipids; D008081:Liposomes; D039821:Monoterpenes; D008610:Menthol; C024098:6-carboxyfluorescein; D013943:Thymol; C074463:linalyl acetate