CONICET | Buscador de Institutos y Recursos Humanos

In the last years, the emergence of multidrug-resistant pathogens has become a seriousproblem in public health. This situation has brought attention to antimicrobial peptides,as an alternative to conventional drugs. These compounds usually exert theirantimicrobial activity through the permeabilization of the bacterial membrane, hence, itis important to study this process for their characterization.In the present work, we characterized the permeabilization induced by two ?de novo?designed peptides P1 (WPKWWKWKRRWGRKKAKKRRG) and P6.2(GLLRKWGKKWKEFLRRVWK) in bacterial membranes. Their antimicrobial activity waspreviously tested in Staphylococcus aureus and Escherichia coli strains, having gotten aMIC value of 32 μM and 128 μM respectively for P1; 12,72 μM for both strains in the caseof P6.2.The permeabilization analysis of the outer membrane in E. coli and the plasmaticmembrane in S. aureus showed both peptides can damage the membrane. EC50 valuesand Hill coefficients show higher cooperativity for P6.2 which could partially explain itslower MIC values for both strains. The kinetics study of the process showed a fasterprocess for E. coli, even for the P1 which exhibited a higher MIC value. The innermembrane permeabilization in E. coli also showed a higher rate in P6.2, but in this case,the EC50 values for both peptides are better correlated with MICs value. Finally,fluorescence microscopy was able to confirm the global permeabilization of the bacterialenvelopes.From the results we got, we can conclude that, even though outer membranepermeabilization in E. coli is faster than S. aureus, correlation with MIC values seems tobe more important with the process of permeabilization of its inner membrane. As for thegram-positive S. aureus, MIC values correlate with plasmatic permeabilization correctly.Also, the results obtained showed that the kinetics of the permeabilization process is animportant factor in the final lethal activity of the peptides.

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