THE MORPHOLOGICAL EFFECTS OF 2 ANTIMICROBIAL PEPTIDES, HECATE-1 AND MELITTIN, ON ESCHERICHIA-COLI

The effects of the 26 amino acid, cationic, amphipathic, antibacterial peptide melittin and hecate-1, a 23 amino acid analog of it, on the g ram negative bacterium Escherichia coli were investigated using scanni ng electron microscopy (SEM), transmission electron microscopy (TEM), and freeze-fracture. Both peptides killed virtually all bacteria at th e peptide concentration and cell density used. TEM and SEM revealed ag gregates of bacteria entangled with material extruded from the bacteri al surfaces. SEM revealed irregular bacterial surfaces with bleb-like projections. TEM and freeze-fracture indicate that the bacterial inner and outer membranes, as well as the peptidoglycan layer between, were extensively damaged. The cytoplasmic contents of the cells, however, did not appear radically disturbed, providing little evidence for osmo tically induced cytolysis.