ULTRASTRUCTURE OF BACTEROIDES SPECIES - BACTEROIDES-ASACCHAROLYTICUS, BACTEROIDES-FRAGILIS, BACTEROIDES-MELANINOGENICUS SUBSPECIES MELANINOGENICUS, AND B MELANINOGENICUS SUBSPECIES INTERMEDIUS

Representative strains of two subspecies of Bacteroides melaninogenicus (subspecies melaninogenicus and subspecies intermedins) and Bacteroides asaccharolyticus as well as B. asaccharolyticus strain 536B isolated from a human perirectal abscess and Bacteroides fragilis ATCC 25285 were examined by glutaraldehyde-osmium fixation, ruthenium red fixation and staining, and thorium hydroxide staining as well as by the physical preparative techniques of critical point drying-transmission electron microscopy (CPD-TEM) and scanning electron microscopy (SEM). All strains, with the exception of B. fragilis 25285, possessed an electron-dense material external to their outer membranes. Ruthenium red staining further revealed a layer, external to the surface of the outer membrane, that was distinct for each species examined. Thorium hydroxide, as well as CPD-TEM and SEM, showed the cells to be interconnected by thin fibers that not only connected adjacent cells but also traversed several microns to connect cell aggregates. © 1979 by The University of Chicago.