<prompt> 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 beScrappings from ulcer for culture on chocolate agar with antibiotic supplementSerology from detection of specific IgM antibodiesScrappings from ulcer for dark field microscopyScrappings from ulcer for tissue culture  <response>: Clues are:-Painless ulcerSingle lesionIt 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. 