A 30-year-old man comes to the clinic because of a painful ulcer on his penis for the past week. He has had multiple sexual partners, including commercial sex workers. Physical examination shows lymphadenopathy in the inguinal region and a 1-cm tender ulcer with no induration located on the frenulum. A culture of the ulcer grows colonies on supplemented chocolate agar. A Gram stain of the colonies shows gram-negative coccobacilli. Which of the following is the most likely causal organism?
Haemophilus ducreyi
Herpes simplex virus
Neisseria gonorrhoeae
Treponema pallidum
Trichomonas vaginalis
Correct answer
Haemophilus ducreyi
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correct answer: A
Haemophilus decreyi (choice A) is a Gram-negative coccobacillus that is typically grown on chocolate agar. Like the other answer choices, it is a sexually transmitted disease, but it is characterized by painful lesions in the genitalia.
Herpes simplex virus (choice B), like other viruses, cannot be Gram stained. The test of choice for identifying a herpes virus is a Tzanck test.
Neisseria gonorrhoeae (choice C) is a Gram-negative diplococci.
Treponema pallidum (choice D) is the bacteria that causes syphilis and is a spirochete. Trichomonas vaginalis (choice E) parasitic flagellated protozoan.