Bacteriology USMLE Step 1 Practice Question
A 23-year-old female with sickle cell disease presents with fever (39.2°C), severe left tibial pain, and tachycardia (HR 108/min). Blood pressure is 118/76 mmHg, respirations 18/min, and SpO2 98% on room air. X-ray demonstrates a lytic lesion of the tibia. Blood cultures and bone culture both grow gram-negative rods. WBC is elevated at 14,200/μL with left shift. She denies recent gastrointestinal or genitourinary symptoms. Which organism best explains this clinical presentation?
Answer choices
- AIt is comma-shaped and sensitive to acidic pH.
- BIt is an obligate intracellular parasite.
- CIt is motile and does not ferment lactose.Correct answer
- DIt is a nonmotile facultative anaerobe.
- EIt is motile and oxidase positive.
- FIt is a gram-positive rod that produces beta-hemolysis on blood agar.
See the full explanation
Get the correct-answer rationale, why each distractor is wrong, the underlying mechanism, and high-yield associations — plus adaptive practice that targets your weak areas — with a free MedBoardPRO account.