How does syphilis typically appear under microscopic examination?

Syphilis is caused by the bacterium Treponema pallidum, which has a distinctive appearance when examined under a microscope. Treponema pallidum is a spirochete, which means it is characterized by its coiled, spiral shape. This unique morphology allows it to exhibit corkscrew motility, an important feature that aids in its movement through viscous environments like bodily tissues.

Under dark field microscopy, Treponema pallidum is observed to appear as fine, spiral organisms. This specific morphology is essential for the identification of the organism in laboratory settings and helps to confirm a diagnosis of syphilis. Corkscrew motility is a key aspect of its identification, as it distinguishes it from other types of bacteria that may have different shapes or motility patterns.

In contrast to this, other shapes described in the choices, such as straight rods or larger spherical organisms, do not accurately reflect the structure of Treponema pallidum, and would typically suggest alternative bacterial or microbial species. Thus, the unique spiral structure and corkscrew motion of the organism are what make the identification of syphilis so specific.