Bacteriology USMLE Step 1 Practice Question
A 72-year-old man on chemotherapy presents with fever (39.2°C), confusion, and neck stiffness two weeks after consuming unpasteurized cheese. Vital signs show HR 108, BP 136/82, RR 20, SpO2 98% on room air. Blood culture grows small gram-positive rods with characteristic tumbling motility. CSF analysis reveals elevated protein (180 mg/dL) and lymphocytic pleocytosis. No rash is noted. Which virulence mechanism enables this organism's direct cell-to-cell movement without extracellular phase?
Answer choices
- AFormation of an antiphagocytic capsule made of hyaluronic acid
- BProduction of urease to increase local pH
- CPolymerization of host actinCorrect answer
- DRelease of a toxin that cleaves SNARE proteins
- EBlockade of phagolysosome fusion by sulfatides
- FSecretion of internalins that bind to E-cadherin on host cells
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