Bacteriology USMLE Step 1 Practice Question
A 42-year-old woman with a 10-year history of systemic lupus erythematosus presents to the emergency department with a 3-day history of dysuria, frequency, and left flank pain. She denies vaginal discharge or previous urinary tract infections. Temperature is 39.1°C, blood pressure 126/80 mmHg, heart rate 104/min, and respiratory rate 18/min. Urinalysis shows leukocyte esterase positive, nitrite negative, pH 8.2, and 18 WBCs/hpf with no bacteria on Gram stain. Urine culture grows a gram-negative rod that is oxidase negative, lactose non-fermenting, hydrogen sulfide positive, and produces a characteristic musty/earthy odor on agar plates. Blood cultures remain sterile after 48 hours. Which organism is most likely responsible for this patient's pyelonephritis?
Answer choices
- APseudomonas aeruginosa
- BKlebsiella pneumoniae
- CProteus mirabilisCorrect answer
- DSerratia marcescens
- EEscherichia coli
- FSalmonella typhi
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