Treponema pallidum is a spirochaete bacterium.

There are at least three known subspecies, T. pallidum pallidum, which causes syphilis; T. pallidum pertenue, which causes yaws; and T. pallidum endemicum, which causes bejel .

It is a motile spirochaete that is generally acquired by close sexual contact.

Treponema pallidum enters the host via breaches in squamous or columnar epithelium.

Primary infection is normally via sexual contact. Rarely, it may occur in medical personnel.

Treponema pallidum can be transmitted to a fetus by transplacental passage during the later stages of pregnancy giving rise to congenital syphilis.

In the July 17, 1998 issue of the journal Science, a group of biologists reported how they sequenced the genome of T. pallidum.