Treponema pallidum cannot be cultivated in routine laboratory media. The cardinal laboratory confirmation of primary syphilis (chancre stage) is therefore best achieved by:

• A VDRL test — rapid plasma reagin for anti-cardiolipin antibodies
• B FTA-ABS (fluorescent treponemal antibody absorbed test) on serum
• C Polymerase chain reaction for treponemal DNA on blood
• D Dark-field microscopy of serous exudate from the chancre, demonstrating characteristic motile spirochetes with corkscrew morphology and approximately 8–14 regular coils ✓

Explanation

In primary syphilis, the VDRL/RPR may be seronegative in up to 30% of cases (early primary infection, within 1–2 weeks of chancre appearance). Dark-field microscopy of scrapings from the base of the chancre directly visualizes motile T. pallidum — thin, tightly coiled spirochetes with characteristic slow rotation and flexion about the midpoint. This is the most rapid definitive test for active primary syphilis. The test cannot be used for oral/rectal lesions due to confusion with commensal treponemes.

Reference: Ananthanarayan & Paniker's Textbook of Microbiology, 11th ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

Written and medically reviewed by the StethoPrep medical team.