WBR0382

Author	[[PageAuthor::Yazan Daaboul, M.D. (Reviewed by Yazan Daaboul, M.D.)]]
Exam Type	USMLE Step 1
Main Category	Microbiology
Sub Category	Genitourinary
Prompt	A 38-year-old man presents to the emergency department with complaints of fever and back pain that radiates to the inguinal area. His temperature of 38.5 °C (101.3 °F), heart rate is 98/min, and blood pressure is 122/88 mmHg. Following appropriate work-up, the patient is diagnosed with struvite kidney stone. Urine cultures demonstrate a urea-splitting organism with swarming motility. Which of the following characteristics most likely correspond to the organism responsible for this patient's symptoms?
Answer A	Oxidase-positive, catalase-positive, urease-positive
Answer A Explanation	Proteus mirabilis is oxidase-negative.
Answer B	Oxidase-negative, catalase-negative, urease-positive
Answer B Explanation	Proteus mirabilis is catalase-positive.
Answer C	Oxidase-positive, catalase-negative, urease-negative
Answer C Explanation	Proteus mirabilis is oxidase-negative, catalase-positive, and urease-positive.
Answer D	Oxidase-negative, catalase-positive, urease-positive
Answer D Explanation	Proteus mirabilis is correctly an oxidase-negative, catalase-positive, urease-positive, gram-negative rod.
Answer E	Oxidase-positive, catalase-positive, urease-negative
Answer E Explanation	Proteus mirabilis is oxidase-negative and urease-positive.
Right Answer	D
Explanation	Proteus mirabilis is the most common causative agent of struvite stones. It is an oxidase-negative, catalase-positive, urease-positive, gram-negative rod that has a characteristic “swarming” motility in cultures. Proteus mirabilis is a known pathogen of the urogenital tract. Other examples of urea-splitting organisms are Pseudomonas, Klebsiella, Staphylococcus, and Mycoplasma. Educational Objective: Proteus mirabilis is a common causative agent of struvite stones. It is an oxidase-negative, catalase-positive, urease-positive, gram-negative rod with characteristic “swarming” motility in culture. References: First Aid 2014 page 173
Approved	Yes
Keyword	Proteus mirabilis, Struvite stones, Oxidase, Catalase, Urease, Gram negative, Rod, Swarming motility
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