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An outer membrane-disorganizing peptide PMBN sensitizes E. coli strains to serum bactericidal action
Abstract:
The small cationic outer membrane-disorganizing peptide PMBN sensitized four smooth, encapsulated strains of Escherichia coli (serotypes 02:K1, 04:K12, 018:K1, and 018:K5) to the lethal action of serum. The concentrations of PMBN required were low (0.3 to 1.0 microgram/ml). One E. coli strain (IH 11030; 075:K5) remained virtually resistant to serum and also to anti-075 hyperimmune serum plus complement (C) even in the presence of PMBN. This strain was nevertheless sensitive to the outer membrane permeability-increasing action of PMBN. In the bactericidal system, PMBN could be replaced by high concentrations of lysine20 or protamine but not lysine4. The PMBN-dependent bactericidal activity of GPS was abolished by heating or zymosan treatment that inactivate its C but not by lack of the action of the classical pathway of the C in C4-deficient GPS. PMBN formed a bactericidal system also with normal rabbit, rat, and human serum but not with mouse serum. The bactericidal system against E. coli 018:K1 and its derivative EH 817 (018:K1-) was found to require a factor that can be removed from normal sera by absorption with a rough E. coli strain. This factor could be replaced by specific anti-018 antibodies. The bactericidal activity of fetal calf serum plus PMBN against E. coli 018:K1 was enhanced by normal rabbit or anti-E. coli 018 hyperimmune serum. We suggest that PMBN unshields the deep structures and the hydrophobic membrane milieu of the outer membrane and facilitates the insertion of the membrane attack complex of the C into this milieu.
Insights
The peptide PMBN (palytoxin-like membrane-binding peptide) enhances serum killing of Escherichia coli by disrupting its outer membrane. This peptide sensitizes bacteria to complement-mediated lysis, offering a potential therapeutic strategy against infections.
Area of Science:
- Microbiology
- Immunology
- Biochemistry
Background:
- The outer membrane of Gram-negative bacteria like Escherichia coli presents a barrier to antimicrobial agents.
- Certain peptides can interact with and disrupt bacterial outer membranes.
Purpose of the Study:
- To investigate the ability of the peptide PMBN to sensitize encapsulated Escherichia coli strains to serum-mediated killing.
- To elucidate the mechanism by which PMBN enhances serum bactericidal activity.
Main Methods:
- Testing the bactericidal activity of serum in the presence of PMBN against various strains of Escherichia coli.
- Investigating the role of complement components and antibodies in the PMBN-mediated sensitization.
- Assessing the effect of PMBN on outer membrane permeability.
Main Results:
- PMBN significantly sensitized four out of five tested smooth, encapsulated Escherichia coli strains to serum killing at low concentrations.
- One strain remained resistant to serum even with PMBN, despite showing sensitivity to PMBN's membrane-disrupting effects.
- PMBN's bactericidal activity was dependent on complement (C) and required a factor present in normal sera, which could be replaced by specific antibodies.
Conclusions:
- PMBN effectively sensitizes encapsulated E. coli to serum bactericidal activity, likely by disrupting the outer membrane and facilitating complement membrane attack complex insertion.
- PMBN's activity is dependent on complement and specific bacterial surface structures, suggesting potential for targeted antimicrobial strategies.