Step 1 Question of the Week – 10/19/20

This week’s USMLE Step 1 question comes from the area of clinical bacteriology.  See if you can answer the question and then watch the video to learn the correct answer as well as the rationales for all of the options.  The video comes from a recent edition of the Rx Question Lab, so if you like it, we encourage you to register and tune in every Tuesday.

A 31-year-old man comes to his physician’s office with a report of pain on urination for the past day. The patient also reports yellow-white discharge from the urethra. He is sexually active, occasionally uses condoms, and mentions that he has had three sexual partners in the last month. He denies fevers, chills, changes in weight, new rashes, and tingling/numbness in the extremities. The patient’s temperature is 37.5°C (99.5°F), pulse is 88/min, respirations are 14/min, and  blood pressure is 135/70 mm/Hg. Physical examination does not reveal any tender lymph nodes, rashes, or skin lesions. The patient has full range of motion of his joints and normal strength and reflexes in all extremities. Urinalysis reveals:

Color: yellow
Appearance: clear
Specific gravity: 1.012
pH: 7.0
Protein: negative
Glucose: negative
Ketones: negative
Bilirubin: negative
Urobilinogen: normal
Blood: negative
Leukocytes: negative
Nitrite: negative
WBC: 1
RBC:  2
Bacteria: rare
Casts: 1 hyaline cast

Gram staining of the urethral discharge is shown in the image.

Which of the following describes a component of the most likely causative organism?

A. A helical shape with two cell membranes and flagella trapped between them

B. A polysaccharide capsule with the ability to ferment maltose

C. An infectious extracellular form and an intracellular form capable of replication

D. Antigenically variable pili

E. The ability to metabolize urea into ammonia and carbon dioxide

We invite you to leave a comment with your answer as well as your rationale.  When you’re ready to check your work, watch the video.

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