What is the size range of Treponema pallidum?

• A. 0.5-1 µm long and 2-3 µm wide
• B. 50-100 µm long and 1-2 µm wide
• C. 5-20 µm long and 0.1-0.2 µm wide
• D. 0.05-0.1 µm long and 0.5-1 µm wide

Answer: (C)

Treponema pallidum is a slender spirochete, a spiral-shaped bacterium with a very small diameter. Its length is typically a few micrometers, around 5–20 µm, and its width (diameter) is about 0.1–0.2 µm. This combination of a long, thin body fits what we know about this organism and helps explain its ability to move in viscous environments and penetrate tissues. Among the options, the range of 5–20 µm in length and 0.1–0.2 µm in width matches established measurements for T. pallidum. The other ranges imply either lengths that are far too short or too long, or widths that don’t align with how thin these spirochetes are.