Treponema pallidum is the organism responsible for syphilis. Here, it is seen through a dark-field microscope as a tightly coiled simple bacteria. It is a member of the Spirochete family of bacteria.

Primary syphilis. Lesion begins as papule that undergoes ischemic necrosis and erodes to form a 0.3- to 2.0-cm, painless to tender, hard, indurated ulcer. Base clean with scant yellow serous discharge.

Secondary syphilis, with the characteristic findings of pink oval scaly patches on the palm with slight hyperpigmentation. These findings may also be seed the plantar feet.