USMLE Step 1 Question 368

Question:

A 29 year old sexually active woman comes into your office complaining of a “fishy smelling” discharge coming from her vagina for the past few days. She denies any dysuria or inflammation. She has been diagnosed and treated for gonorrhea in the past. On exam, you identify a thin, grayish-white discharge that coats the vaginal walls. You take a culture and send it to the lab. It is reported that there are clue cells on saline wet mount. What organism is most likely responsible for this woman’s symptoms?

Correct Answer: B.  Gardnerella vaginalis

G. vaginalis (choice B) is a pleomorphic rod that causes bacterial vaginosis. It is typically found in sexually active women and is commonly asymptomatic. The most common presenting symptom is a homogenous, thin, grayish-white discharge from the vagina.

The diagnosis is made by the identification of clue cells on saline wet mount. Clue cells are vaginal epithelial cells covered with bacteria.

C. trachomatis (choice A) and N. gonorrhoeae (choice C) are common sexually transmitted infections, but these would most likely present with a painful discharge and there would most likely be no clue cells.

S. aureus (choice D) is part of the normal skin flora. It can cause inflammatory processes such as skin infections or abscesses, as well as toxin-mediated disease. Toxic shock syndrome should be suspected in women who wear tampons when menstruating.

S. agalactiae (choice E), also known as group B streptococci, frequently colonizes the human genital tract. It can be vertically transmitted from mother to child, causing neonatal sepsis and meningitis.