Susceptibility of Legionella gormanii Membrane-Derived Phospholipids to the Peptide Action of Antimicrobial LL-37-Langmuir Monolayer Studies.

LL-37 is the only member of the cathelicidin-type host defense peptide family in humans. It exhibits broad-spectrum bactericidal activity, which represents a distinctive advantage for future therapeutic targets. The presence of choline in the growth medium for bacteria changes the composition and physicochemical properties of their membranes, which affects LL-37's activity as an antimicrobial agent. In this study, the effect of the LL-37 peptide on the phospholipid monolayers at the liquid-air interface imitating the membranes of Legionella gormanii bacteria was determined. The Langmuir monolayer technique was employed to prepare model membranes composed of individual classes of phospholipids-phosphatidylcholine (PC), phosphatidylethanolamine (PE), phosphatidylglycerol (PG), cardiolipin (CL)-isolated from L. gormanii bacteria supplemented or non-supplemented with exogenous choline. Compression isotherms were obtained for the monolayers with or without the addition of the peptide to the subphase. Then, penetration tests were carried out for the phospholipid monolayers compressed to a surface pressure of 30 mN/m, followed by the insertion of the peptide into the subphase. Changes in the mean molecular area were observed over time. Our findings demonstrate the diversified effect of LL-37 on the phospholipid monolayers, depending on the bacteria growth conditions. The substantial changes in membrane properties due to its interactions with LL-37 enable us to propose a feasible mechanism of peptide action at a molecular level. This can be associated with the stable incorporation of the peptide inside the monolayer or with the disruption of the membrane leading to the removal (desorption) of molecules into the subphase. Understanding the role of antimicrobial peptides is crucial for the design and development of new strategies and routes for combating resistance to conventional antibiotics.

Changes in wetting properties of alumina surface treated with DPPC in the presence of phospholipase A2 enzyme.

Wetting properties of commercial Al(2)O(3) plates contacted with dipalmitoylphosphatidylcholine (DPPC) or DPPC+enzyme (phospholipase PLA(2)) in NaCl solution were determined by thin layer wicking and with the help of Washburn equation. Van Oss et al.'s approach to interfacial free energy interactions was applied to determining the solid surface free energy components. Wicking experiments were performed both for bare and alumina plates precontacted overnight with the probe liquid saturated vapours, as well as the untreated and DPPC (or DPPC+PLA(2)) treated alumina plates. For this purpose the penetration rates of n-octane, water and formamide were measured. From these experiments it resulted that original alumina surface is strongly polar with electron-donor interactions originating from the surface hydroxyl groups. Adsorption of DPPC on Al(2)O(3) plates slightly increased the hydrophobic character of the alumina surface (considerable decrease of the electron-donor, γ(s)(-) parameter and γ(s)(AB) component was visible) in such a way that the hydrocarbon chains were directed outwards and the polar part towards the alumina surface. However, after the enzyme action the products of DPPC hydrolysis by PLA(2) (palmitic acid and lysophosphatidylcholine) increased again the hydrophilic character of Al(2)O(3) surface (a minor increase in γ(s)(AB) component and drastic increase of the electron-donor γ(s)(-) parameter was noticeable). After treatment with DPPC or DPPC+enzyme PLA(2) solution the changes of the total surface free energy of alumina and its Lifshits-van der Waals (γ(s)(LW)) component were in the range 7-10 mJ/m(2), but the most considerable and delivering more interesting information were the changes of the electron-donor (γ(s)(-)) parameter ranging from 27 to 35 mJ/m(2). Moreover, the changes of the alumina surface wettability were dependent on the time of the enzyme contacting with DPPC in NaCl solution. On the basis of the obtained results it seems that the thin layer wicking method can be an additional useful tool in investigations of the effect of phospholipid and PLA(2) action on the hydrophilic-hydrophobic character of alumina surface.