A 35-year-old male presents with a single, painful, deep, undermined genital ulcer with ragged borders and a gray exudate. He also has tender, unilateral inguinal lymphadenopathy that is fluctuant. Which of the following is the most likely causative organism?

Explanation

This clinical presentation is classic for chancroid. Chancroid, caused by Haemophilus ducreyi, typically presents as a single (though sometimes multiple), painful, deep genital ulcer with undermined, ragged borders and a gray or yellowish exudate. It is often accompanied by painful, unilateral inguinal lymphadenopathy that can become fluctuant (bubo formation). Treponema pallidum causes syphilis, which presents as a painless chancre. Herpes simplex virus type 2 causes multiple, painful, superficial vesicles that evolve into ulcers. Chlamydia trachomatis serovars L1, L2, L3 cause Lymphogranuloma Venereum (LGV), which typically starts with a transient, often unnoticed, painless ulcer or papule, followed by severe, painful, often bilateral inguinal lymphadenopathy (buboes) that can rupture.