Which of the following is not correct regarding spirochetes?

• A. Motility is via axial filaments.
• B. Spirochetes are gram positive.
• C. They are visualized best using dark field or phase optics.
• D. Those associated with human disease are 0.1-0.5 μm in diameter and 5-30 μm in length.

Answer: (B)

Spirochetes move with axial filaments (endoflagella) that lie between the inner and outer membranes, producing a distinctive corkscrew motion that helps them move through viscous environments and host tissues. They are typically Gram-negative organisms, not Gram-positive, which is why the statement claiming they are Gram-positive is not correct. Because they are such slender, coiled bacteria, they are best seen in specimens using dark-field or phase-contrast microscopy rather than standard light microscopy with Gram staining. When associated with human disease, they are very small in diameter and long in length, about 0.1–0.5 μm across and 5–30 μm long, which fits their recognizable, threadlike appearance under suitable visualization.