Molecular basis of bacterial outer membrane permeability.

INTRODUCTION Bacteria produce cell walls with the exception of mycoplasmas, and the cell wall component common to all eubacteria is the murein, or the peptidoglycan, which contributes mechanical rigidity. All gram-negative bacteria contain an additional layer in the cell wall structure, i.e., the outer membrane, which is located outside the peptidoglycan layer and shows up as a trilaminar structure on the electron micrographs of thin sections of these bacteria (84). It is becoming increasingly clear that the outer membrane is very important in the physiology of gram-negative bacteria in making them resistant to host defense factors such as lysozyme, P-lysin, and various leukocyte proteins, which