The effect of major terpenes of the hop essential oil on the mixed monolayers and bilayers imitating bacteria membranes. In search of the natural pesticides.

Abstract

From the point of view of environmental problems, the search of the natural antimicrobial agents for various applications, including agriculture, is highly important. In this paper the studies on the effect of β-myrcene and α-humulene on the mixed monolayers and bilayers imitating bacteria membranes were done and the in vitro tests on plant pathogen bacteria Pseudomonas syringae pv. lachrymans PCM 1410 were performed. These terpenes are the main components of the hop essential oil, for which strong potential against phytopathogenic bacteria was confirmed. Thus, the studies were aimed at determining the terpene, which is responsible for antibacterial effect of total extract. During experiments the surface pressure-area measurements, penetration studies and Brewster angle microscopy (BAM) studies on the lipid monolayers were performed and hydrodynamic diameter, zeta potential and steady-state fluorescence anisotropy measurements of liposomes were done. As it was found, both terpenes change the organization of model membranes and make them less stable. Although humulene is of stronger ability to incorporate into the studied systems, neither humulene nor myrcene determine the strong penetration effect observed for the hop essential oil. Moreover, the action of both terpenes on membranes is connected with the partial extraction of the monolayer material from the interface. It was concluded that both terpenes used separately do not act on bacteria membrane as effectively as the hop essential oil and they are not directly responsible for antimicrobial effect of the total extract. However, they may change membrane organization and the same facilitate the incorporation of other active substances into the cell.