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Syphilis Treponema PallidumTreponema pallidum Syphilis is caused by the spirochete Treponema pallidum. Nonpathogenic treponemes can be found in the oral cavity. The unicellular organisms are thin and coiled. The ends of the cells are tapered, and three fibrils are inserted into each end. The organism moves with a drifting rotary motion and usually has a characteristic undulating movement about its center. The outer lipoprotein membrane contains lipopolysaccharide, and a phospholipid-rich outer membrane contains relatively few surface-exposed proteins. The composition of its lipid outer surface, which is similar to that of human cells, and the relative paucity of extruding proteins have important roles in allowing this microorganism to often escape effective immune control and establish a chronic infection. T. pallidum has a primitive genome that has remained stable and constant. This may explain why it has remained as sensitive to penicillin as it was when penicillin was first was introduced. T. pallidum cannot be cultivated on artificial media. There has been some success growing T. pallidum in tissue culture. The organism can be isolated for research purposes by inoculating chimpanzees or rabbit testes. Organisms remain motile in enriched media for up to 7 days at 35 degrees C. |