A 45-year-old woman passes a branched calculus filling her entire right renal pelvis and calyces. Urine culture grows an organism producing copious amounts of urease. Which organism and stone composition pair is most consistent?
- A Escherichia coli and calcium oxalate
- B Proteus mirabilis and magnesium ammonium phosphate ✓
- C Pseudomonas aeruginosa and cystine
- D Klebsiella pneumoniae and uric acid
Correct answer: B. Proteus mirabilis and magnesium ammonium phosphate
Explanation
Staghorn calculi are typically composed of struvite, magnesium ammonium phosphate, which forms when urine becomes alkaline through urease activity of infecting organisms. Proteus species, especially Proteus mirabilis, are the classic urease producers. Escherichia coli is a common cause of urinary infection but does NOT produce urease and is associated with calcium oxalate stones. Cystine stones occur in cystinuria and uric acid stones form in acidic urine, neither related to infection.
Reference: Smith's General Urology, 19th ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
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