Question

A truck driver presented with a painless, demarcated ulcer on penis with inguinal lymphadenopathy. What is the best method of visualization of motility of the probable causative agent?

• A. Dark field microscopy
• B. Light microscopy
• C. Fluorescent microscopy
• D. Electron microscopy

Answer 1

The Correct Option is A

The scenario describes a patient with a classic presentation of a painless, demarcated ulcer on the penis and inguinal lymphadenopathy. These symptoms are highly suggestive of a primary syphilitic chancre, caused by the bacterium Treponema pallidum. To confirm the diagnosis, the best method to visualize the motility of Treponema pallidum is through dark field microscopy. This technique is used to observe spirochetes, like Treponema pallidum, directly in samples taken from the ulcer.

Dark field microscopy is preferred because:

• Treponema pallidum is too thin to be easily seen with light microscopy without staining.
• It cannot be easily cultivated in vitro like many other bacteria.
• Fluorescent microscopy requires specific fluorescent dyes, which are less direct.
• Electron microscopy is not used for routine diagnosis as it requires more complex preparation and equipment.

The process involves placing a sample of the fluid from the ulcer onto a slide and examining it under a dark field microscope, where the spirochetes will appear bright against a dark background, due to their reflective properties. This visualization method clearly illustrates the motility of the spirochetes and confirms their presence.