Ultrastructure of the outer layer and vesicles formed by the outer membrane of the Prevotella intermedia cell

Abstract

We studied the normal in vitro ultrastructure of Prevotella intermedia cells to understand what changes occur in this ultrastructure as a result of host infection. Five strains of P. intermedia and one of Porphyromonas gingivalis were used. TEM samples were prepared from bacterial cells in broth, by spreading broth on agar plates and from colonies grown on agar plates. These samples were fixed by GA-OsO₄, Kellenberger-Ryter solution (KR), GA-OsO₄ containing tannic acid (TA), GA-OsO₄ containing ruthenium red (Ru) and freeze substitution using OsO₄-acetone (FS).
All strains had an outer layer ultrastructure consisting of an inner membrane, periplasmic space, peptidglycan layer, periplasmic space, outer membrance, electron dense layer and fibrous structure From the cytoplasm. Ru, TA and FS were effective in fixing the electron dense layer and fibrous structure, while FS and KR were effective in fixing the cytoplasm.
It was found that the outer layer of P. intermedia cells consists of seven layers and many vesicles are formed by the outer membrane. The width of each layer can be accurately measured on electron micrographs fixed by FS.