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BIO NMDCAT Sexually transmitted diseases
nmdcat.online July 16, 2026

A diagnostic challenge with Treponema pallidum is its inability to be cultured on standard agar media. During laboratory investigation, the most definitive immediate observation of the live organism from a primary chancre exudate is achieved using:

A. Gram staining
B. Dark-field microscopy
✓
C. Electron microscopy
D. Simple iodine staining

📝 Explanation

The correct option is Dark-field microscopy. T. pallidum is too thin to be seen with standard bright-field microscopy and Gram stains poorly. Dark-field microscopy illuminates the live, motile spirochetes against a dark background, allowing immediate identification.

📖 Additional Information

  • Gram staining
  • Dark-field microscopy
  • Electron microscopy
  • Simple iodine staining

The correct option is Dark-field microscopy. T. pallidum is too thin to be seen with standard bright-field microscopy and Gram stains poorly. Dark-field microscopy illuminates the live, motile spirochetes against a dark background, allowing immediate identification.

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