Bacteriology: Proteus and struvite stones: practice question

A Microbiology question in the style of the NEET PG paper. Answer it first, then read why the right option is right and why each of the others is wrong.

Try it

Microbiology · Bacteriology: Proteus and struvite stones

Sample item

A 45-year-old woman with recurrent urinary infections has flank pain, urine pH 8.5 and a staghorn calculus on imaging. Urine culture shows swarming growth on blood agar and non-lactose-fermenting colonies on MacConkey agar. Which bacterial enzyme drives the stone formation?

AUreaseBLecithinaseCPhenylalanine deaminaseDCoagulase

Original practice item, not a recalled exam question. Nothing here is recorded.

The answer and the reasoning

A. Urease

Proteus mirabilis produces urease, which splits urea into ammonia and carbon dioxide, raising urine pH and precipitating magnesium ammonium phosphate and carbonate-apatite as struvite staghorn stones. These stones harbour bacteria, so complete removal is needed in addition to antibiotics.

Option by option

A. Urease (correct)
Correct. Urease-induced alkalinisation precipitates struvite.
B. Lecithinase
Lecithinase, the alpha toxin of Clostridium perfringens, damages cell membranes and is not involved in stone formation.
C. Phenylalanine deaminase
Phenylalanine deaminase is a laboratory identification feature of the Proteus group but does not alkalinise urine.
D. Coagulase
Coagulase clots plasma in Staphylococcus aureus and does not alter urine pH.

Source note: Original NextPrep sample item — pending expert review. This item is original practice material awaiting independent expert review, so confirm important facts in a standard textbook.

Questions about this Microbiology question

What is the answer to this Microbiology question?

The best answer is A, Urease. Proteus mirabilis produces urease, which splits urea into ammonia and carbon dioxide, raising urine pH and precipitating magnesium ammonium phosphate and carbonate-apatite as struvite staghorn stones.

Why is "Lecithinase" not the answer?

Lecithinase, the alpha toxin of Clostridium perfringens, damages cell membranes and is not involved in stone formation.

Why is "Phenylalanine deaminase" not the answer?

Phenylalanine deaminase is a laboratory identification feature of the Proteus group but does not alkalinise urine.

Why is "Coagulase" not the answer?

Coagulase clots plasma in Staphylococcus aureus and does not alter urine pH.

What concept does this question test?

It tests Bacteriology: Proteus and struvite stones in Microbiology. These stones harbour bacteria, so complete removal is needed in addition to antibiotics.

How hard is this question?

We tag it as an application question: it asks you to use a fact on a patient or a finding. The tag is our own editorial judgement, not an official difficulty rating, so read the reason for every option, not only the answer.

How should I study Bacteriology: Proteus and struvite stones?

Make a one-line identity card for each organism: shape and stain, defining test, toxin, disease and drug. Then use the flashcards and the other Microbiology questions on this site to test what stuck.

Is this a real NEET PG question?

No. It is an original practice item (editorial status: sample, version 1). NextPrep does not publish recalled or leaked questions, and independent faculty review of this item has not been completed yet, so confirm important facts in a standard textbook.