CONICET | Buscador de Institutos y Recursos Humanos

Due to the increase of new mechanisms of resistance of sensitive cells to traditionalantibiotics, it is necessary to develop novel strategies for the control of microbial growth. Inthis sense, antimicrobial peptides represent a valuable alternative, due to their broadspectrum of action. Therefore, the study of the mechanism of action of antimicrobial peptidesin the interaction with biological membranes is of special interest, since this interaction canaffect the properties of the lipid bilayer such as selective permeability and modulate thecurvature of the interface. Certain cationic peptides, such as Polymyxin E or also known asColistin, cause cell death by inserting into the lipid membrane of Gram-negative bacteria by ayet unknown mechanism, acting as antimicrobial agents. To gain knowledge about thisinteraction and the mechanism of action of this peptide at molecular level, we worked withtwo different models of bacterial membranes, On the one hand, we worked with mimeticmembrane models using Langmuir-Blodgett phospholipid monolayers. Langmuir isotherms andfixed area Gibbs isotherms were performed to study the effect of pH and lipid compositionon the interaction with Polymyxin, measuring surface pressure and surface potentialsimultaneously. On the other hand, lipid bilayer models were studied, using medium-sizedunilamellar liposomes or LUVs, in the presence and absence of the peptide by means offluorescence spectroscopy with polarized light. The results of this work indicate that theinteraction of Polymyxin with lipid monolayers is modulated by the charge state of themembrane. It was also demonstrated that the interaction with this peptide influences thedegree of order and fluidity of the lipid bilayers, showing two differentiated order states inboth phases of the lipidic film.

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