Treponema sp. Transmission electron micrograph of sectioned Treponema sp. bacteria (dark grey) attached to the epithelial surface of the human duodenum. Epithelial cell cytoplasm is seen at bottom. These spiral-shaped bacteria (spiro- chaetes) lack rigid cell walls. Pathogenic species of Treponema include T. pallidum which causes syphilis; T. carateum which causes the skin disease pinta" common in tropical America: T. pertenue which causes yaws in Africa. In syphilis, the bacteria may be found on the duodenum of the intestine, as well as in most other parts of the body. Magnification: x58,000 at 8x6 inch size."