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.

First report on rapid screening of nanomaterial-based antimicrobial agents against β-lactamase resistance using pGLO plasmid transformed Escherichia coli HB 101 K-12

“…This is due to the presence of lipophilic outer membrane in Gram-negative bacteria, which acts as a hydrophilic permeability barrier for the entry of hydrophobic compounds such as AKBA (Raja et al 2011;Hancock 1997;Helander et al 1998). Similar observations were made in studies dealing with antibacterial activity of other hydrophobic compounds against Gram-negative bacteria (Trombetta et al 2005;Gallucci et al 2009). …”

Volatile affairs in microbial interactions

“…Indeed, a study on the mechanisms of inhibitory action of three monoterpenes against S. aureus and Escherichia coli revealed a perturbation of the lipid fraction of microorganisms' plasma membrane, resulting in alteration of membrane permeability and a leakage of intracellular compounds (Trombetta et al, 2005).…”

In vitro activity of Origanum vulgare essential oil against Candida species

“…Some studies suggest that the antimicrobial action of essential oils can be a consequence of a negative effect on enzymes, including those involved in the production of energy and synthesis of structural components of the microorganism, in addition to destruction or inactivation of genetic material (14,28).…”

“…Also, alterations in the ion transport processes of the cell membrane and modifications in the activity of calcium channels can cause an increase in cell permeability and consequent release of vital intracellular constituents (28). …”

“…Inhibition of microorganisms by essential oils seems to rely on different mechanisms of action (2,14,26,27,28).…”