<prompt> 23 years old male had unprotected sexual intercourse with a commercial sex worker. Two weeks later, he developed a painless, indurated ulcer on the glans that exuded clear serum on pressure. Inguinal lymph nodes in both groins were enlarged and not tender. The most appropriate diagnostic test is:Grams stain of ulcer dischargeDark field microscopy of ulcer dischargeGiemsa stain of lymph node aspirateELISA for HIV infection  <response>: Ans. is b i.e., Dark field microscopy of ulcer discharge Ref: Harrison, 17the, p. 1384 ,18the, p. 1043 and19the, p. 1132; Ananthanarayan, 9the, p. 370History is indicating towards syphilis and T. pallidum can be seen from ulcer discharge by using Dark field microscopy. 