A plain abdominal radiograph of a 40-year-old woman with recurrent urinary infections shows a large branched calcification filling and outlining the entire renal pelvis and calyces of the left kidney. Which organism is most classically associated with this type of calculus?

• A Escherichia coli
• B Streptococcus faecalis
• C Klebsiella pneumoniae
• D Proteus mirabilis ✓

Explanation

A staghorn calculus is composed of struvite, magnesium ammonium phosphate, and forms in alkaline urine produced by urease splitting organisms. Proteus species are the classic association because urease hydrolyses urea to ammonia, raising urinary pH and precipitating struvite. Escherichia coli does not produce significant urease and is associated with oxalate stones, so it is the most tempting but incorrect distractor here.

Reference: Smith's General Urology, 19th ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

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