Treponema sp. Colour scanning electron micrograph of a colony of bacteria Treponema sp. (blue), attached to the epithelial surface of the human duodenum (pink). Epithelial cell surfaces appear noduled. These elongated spiral-shaped bacteria (spirochaetes) lack rigid cell walls. Pathogenic species of Treponema include T.pallidum which causes syphilis; T. carateum which causes the skin disease pinta" in tropical America; T. pertenue which causes yaws in Africa. In syphilis, the bacteria may be found on the duodenum, as seen here, as well as in most other parts of the body. Magnification: x7,600 at 6x7cm size. 24,000 at 10x8""