A 24-year-old male presents to a STD clinic with a single painless ulcer on external genitalia. The choice of laboratory test to look for the etiological agent would be –: (A) Scrappings from ulcer for culture on chocolate agar with antibiotic supplement, (B) Serology from detection of specific IgM antibodies, (C) Scrappings from ulcer for dark field microscopy, (D) Scrappings from ulcer for tissue culture
Answer is C. Clues are:-


Painless ulcer
Single lesion


It may be either LGV or chance:-

Chancre  → Darkfield microscopy or serological tests (VDRL, FTA-ABS).
IGV → Demonstration of inclusion bodies, fries test, CFT.

Amongst all these tests only darkfield microscopy has been given in the options.
So, I am assuming that it is a case of primary syphilis (chancre), for which dark field microscopy can be used for diagnosis.