Struvite kidney stones are associated with infection by urease-producing organisms and often form staghorn calculi. Which organism is a common cause?

• A. Proteus mirabilis
• B. Escherichia coli
• C. Staphylococcus saprophyticus
• D. Klebsiella pneumoniae

Answer: (A)

Struvite stones form in urine that has become alkaline due to urease-producing bacteria. Urease splits urea into ammonia and carbon dioxide, raising the pH and promoting precipitation of magnesium ammonium phosphate, leading to infection stones that can become large and branching, known as staghorn calculi. Proteus mirabilis is the classic culprit because it has strong urease activity and is frequently involved in urinary tract infections that produce struvite stones. Other common UTI pathogens like Escherichia coli and Staphylococcus saprophyticus don’t typically produce urease and are not as strongly associated with struvite stone formation. Klebsiella can be urease-positive, but Proteus remains the most characteristic cause of these stones.