Damage of the Bacterial Cell Envelope by Antimicrobial Peptides Gramicidin S and PGLa as Revealed by Transmission and Scanning Electron Microscopy

Antimicrobial Agents and Chemotherapy - Tập 54 Số 8 - Trang 3132-3142 - 2010
Mareike Hartmann1, Marina Berditsch1, J. Hawecker2, Mohammad Fotouhi Ardakani2, Dagmar Gerthsen2, Anne S. Ulrich1,3
1Karlsruhe Institute of Technology (KIT), DFG Center for Functional Nanostructures (CFN), Institute of Organic Chemistry, Fritz-Haber-Weg 6, 76131 Karlsruhe, Germany
2Karlsruhe Institute of Technology (KIT), Laboratory for Electron Microscopy, DFG Center for Functional Nanostructures (CFN), Engesserstraße 7, 76131 Karlsruhe, Germany
3Karlsruhe Institute of Technology (KIT), Institute of Biological Interfaces (IBG-2), P.O. Box 3640, 76021, Karlsruhe, Germany

Tóm tắt

ABSTRACTScanning electron microscopy (SEM) and transmission electron microscopy (TEM) were used to examine the ultrastructural changes in bacteria induced by antimicrobial peptides (AMPs). Both the β-stranded gramicidin S and the α-helical peptidyl-glycylleucine-carboxyamide (PGLa) are cationic amphiphilic AMPs known to interact with bacterial membranes. One representative Gram-negative strain,Escherichia coliATCC 25922, and one representative Gram-positive strain,Staphylococcus aureusATCC 25923, were exposed to the AMPs at sub-MICs and supra-MICs in salt-free medium. SEM revealed a shortening and swelling of theE. colicells, and multiple blisters and bubbles formed on their surface. TheS. aureuscells seemed to burst upon AMP exposure, showing open holes and deep craters in their envelope. TEM revealed the formation of intracellular membranous structures in both strains, which is attributed to a lateral expansion of the lipid membrane upon peptide insertion. Also, some morphological alterations in the DNA region were detected forS. aureus. AfterE. coliwas incubated with AMPs in medium with low ionic strength, the cells appeared highly turgid compared to untreated controls. This observation suggests that the AMPs enhance osmosis through the inner membrane, before they eventually cause excessive leakage of the cellular contents. The adverse effect on the osmoregulatory capacity of the bacteria is attributed to the membrane-permeabilizing action of the amphiphilic peptides, even at low (sub-MIC) AMP concentrations. Altogether, the results demonstrate that both TEM and SEM, as well as appropriate sample preparation protocols, are needed to obtain detailed mechanistic insights into peptide function.

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Antimicrobial Agents and Chemotherapy

Tập 54 Số 8

3132-3142

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