Transmission-scanning electron microscopic observations of selected Eikenella corrodens strains

The morphology of Eikenella corrodens 333/54-55 (ATCC 23834) and two human periodontal lesion isolates, strains 470 and 373, was examined by transmission and scanning electron microscopy. All strains exhibited a cell envelope characteristic of gram-negative bacteria. Staining with ruthenium red and alcian blue revealed a loosely organized fibrous slime layer associated with the outer surface of the outer membrane. Slime "stabilization" was achieved by incubation of cells with antisera prepared against whole cells of the Eikenella strains. The stabilized slime appeared as a thick, electron-opaque layer juxtaposed to the outer membrane. Negative staining and heavy metal shadow-casting revealed an interwoven network of fibrils approximately 4 nm in diameter. These fibrils appeared to represent subunits of a larger fibril. Scanning electron microscopy after antibody slime stabilization confirmed the presence and location of the slime layer.