Electron microscopy as an aid in the taxonomic differentiation of oral spirochetes

Abstract

Pure cultures of Treponema microdentium and Borrelia vincentii as well as spirochetes present in normal and pathologically involved gingival sulci were examined by electron microscopy of shadowed and negatively stained preparations and in ultra-thin sections. The spirochetes could be divided into three main groups on the basis of size of the protoplasmic cylinder, structure of the outer envelope and number of axial fibrils originating at one end. The group of “small” spirochetes had a protoplasmic cylinder with a diameter of 100–250 mμ, an outer envelope composed of polygonal structural subunits which was easily disrupted, and either one or two axial fibrils originating at each end of the protoplasmic cylinder. The group of “intermediate” spirochetes appeared essentially similar to the “small” spirochetes except for the diameter of the protoplasmic cylinder which measured from 200–500 mμ and the number of axial fibrils originating near each end which ranged from three to twenty. The “large” spirochetes had a protoplasmic cylinder approximately 500 mμ in dia. and occasionally larger, from the ends of which originated from twelve to more than twenty axial fibrils. These spirochetes were characterized by an outer envelope structurally different from that observed in the other two groups. It is suggested that the ultrastructural characteristics of spirochetes may be used as an aid to their taxonomic differentiation.