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25-04: Dark-Field Examination for Treponema Pallidum

Camiron L. Pfennig; B. Ethan Brown

Uses

To evaluate a lesion (chancre, mucous patch, condyloma lata, skin rash) for the presence of Treponema pallidum.

Materials

Compound microscope with dark-field condenser (dark-field microscope), glass microscope slide, coverslip, and physiologic saline.

Method

  1. From chancre or condyloma lata:

    1. Gently abrade the lesion with a dry gauze.

    2. Dab away any bleeding.

    3. Touch slide to exudative fluid in base of lesion.

    4. Overlay coverslip and view immediately under dark-field microscope using ×40 and ×100 objectives.

  2. From mucous patch:

    1. Touch slide to mucous patch.

    2. Overlay coverslip and view immediately under dark-field microscope using ×40 and ×100 objectives.

  3. From skin lesion:

    1. Gently scrape surface of skin lesion with edge of a number 15 scalpel blade.

    2. Dab away any bleeding.

    3. Touch slide to exudative fluid rising from skin lesion.

    4. Overlay coverslip and view immediately under dark-field microscope using ×40 and ×100 objectives.

FIGURE 25.15

Dark-Field Microscopy. Examined under a dark-field microscope at ×40 or ×100 power, spirochetes appear as motile, bright corkscrews against a black background. (Reproduced with permission, from Morse SA, Holmes KK, Ballard RC, Moreland AA (eds). Atlas of Sexually Transmitted Diseases and AIDS. 4th ed. Saunders Elsevier; 2010. Copyright © 2010 Elsevier, Ltd.)

A slide under the microscope shows white dots and a worm-like white structures on a black background..
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