Treponema pallidum subsp. pertenue Treponema pallidum subsp. endemicum
This chapter addresses the bacteria that belong in the order Spirochaetales. Although there are at least eight genera in this family, only the genera Treponema, Borrelia, and Leptospira, which contain organisms pathogenic for humans, are addressed in this chapter. Although there are two other human intestinal spirochetes identified to date, Brachyspira (Serpulina)pilo-sicoli and Brachyspira aalborgi, that have been isolated from biopsy material from patients with intestinal disease, a clear association between their presence and intestinal disease has not been established. A few cases of intestinal spirochetosis with septicemia and dissemination have been reported thereby providing some support as to a pathogenic role for these organisms.8
The spirochetes are all long, slender, helically curved, gram-negative bacilli, with the unusual morphologic features of axial fibrils and an outer sheath. These fibrils, or axial filaments, are flagella-like organelles that wrap around the bacteria's cell wall, are enclosed within the outer sheath, and facilitate motility of the organisms. The fibrils are attached within the cell wall by platelike structures, called insertion disks, located near the ends of the cells. The protoplasmic cylinder gyrates around the fibrils, causing bacterial movement to appear & a corkscrew-like winding. Differentiation of genera within the family Spirochaetaceae is based on the number axial fibrils, the number of insertion disks present (Table 48-1), and biochemical and metabolic features. "Hie spirochetes also fall into genera based loosely on their morphology (Figure 48-1): Treponema are slender with tight coils; Borrelia are somewhat thicker with fewer and looser coils; and Leptospira resemble Borrelia except for their hooked ends.
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