Transmission electron microscopic observations of membrane effects of antibiotic cecropin B on Escherichia coli

The pathway of cell membrane lysis by the peptide antibiotic cecropin B (CB), which contains both a hydrophobic and an amphipathic α‐helix, was analysed by assessing the morphological changes of Escherichia coli following treatment with the peptide. Exposure of green fluorescent protein (GFP)‐expres...

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Bibliographic Details
Published in:Microscopy research and technique 2003-12, Vol.62 (5), p.423-430
Main Authors: Chen, Hueih Min, Chan, Shiu-Chiu, Lee, Jao-Chang, Chang, Chia-Ching, Murugan, Marudhamuthu, Jack, Ralph W.
Format: Article
Language:English
Subjects:
Animals
Anti-Infective Agents - pharmacology
cecropin B
Cell Membrane - drug effects
Cell Membrane - pathology
Cell Membrane - ultrastructure
defence peptide
Escherichia coli
Escherichia coli - drug effects
Escherichia coli - ultrastructure
Green Fluorescent Proteins
Immunohistochemistry
Insect Proteins - pharmacology
Liposomes - metabolism
Luminescent Proteins
Microscopy, Electron
peptide antibiotic
peptide-membrane interaction
transmission electron microscopy
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Summary:The pathway of cell membrane lysis by the peptide antibiotic cecropin B (CB), which contains both a hydrophobic and an amphipathic α‐helix, was analysed by assessing the morphological changes of Escherichia coli following treatment with the peptide. Exposure of green fluorescent protein (GFP)‐expressing E. coli to CB does not lead to an efflux of GFP. Moreover, transmission electron microscopic (TEM) examination of cecropin B‐treated cells showed that severe swelling precedes cell death and that the outer membrane becomes distended away from the plasma membrane. Using immuno‐gold staining and TEM of E. coli expressing the maltose‐binding protein in the cytoplasm, it was apparent that the protein remains restricted to the cytoplasmic compartment. These observations suggest that CB causes gross disruption of the outer membrane of Gram‐negative bacteria. Circular dichroism measurements of CB in the presence of cell membrane‐mimicking liposomes showed that CB forms secondary structure dependent on the ratio of [lipid]/[peptide]. These observations from this study are important for the future design of custom antimicrobial peptides. Microsc. Res. Tech. 62:423–430, 2003. © 2003 Wiley‐Liss, Inc.
ISSN:1059-910X
1097-0029
DOI:10.1002/jemt.10406