Effects Of The Antimicrobial Peptides On Escherichia Coli And Immunolabeled Receptors On Cell Surface Studied By Atomic Force Microscopy

Atomic force microscopy (AFM) is one of the most important tools and has been extensively used in biology and medicine fields. AFM processes many advantages in life sciences, such as the specimens need not complex pretreatment and can image in near-physiological condition, et al. In the present paper, AFM was used as an important means to study the activity of the antimicrobial peptide on E.coli cells and immune recognition of biomolecules on cell surface.In the first part, the effects of the antimicrobial peptides magainin 2 and melittin on Escherichia coli as target cell were studied by atomic force microscopy, as well as by electron microscopy, fluorescence microscopy, fluorescence spectroscopy, and so on. Nanometer-scale images of the effects of magainin 2 and melittin on the cell morphology were obtained in situ without the use of fixing agents. These high-resolution AFM images of the cells before and after peptide treatment showed distinct changes in cell morphology as a consequence of peptide action. A supplementary mechanism was proposed as the followings:The action of the antimicrobial peptide on E.coli cell was dependent on the particular peptide and as well the peptide concentration. Magainin 2 and melittin transverse the lipopolysaccaride-containing outer membrane of Gram-negative bacteria via a "self-promoted uptake" pathway, and reach the anionic inner membrane. At a low peptide concentration, magainin 2 peptides insert into the inner membrane and induce to form transmembrane pores. Such pores were described as "toroidal-pore" model, resulting in the collapse of the transmembrane electrochemical gradients and the passage of ions and low molecular weight molecules. At a high peptide concentration, magainin 2 bind onto the surface of the membrane, and cover it or part of it in a "carpet-like" manner. When the local peptide concentration is high enough, all peptides act simultaneously and cut the cell across the body.At a low peptide concentration, melittin also induce to form toroidal pores in the...