Bacteriology: Staphylococcus saprophyticus: 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.

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Microbiology · Bacteriology: Staphylococcus saprophyticus

Sample item

A 23-year-old sexually active woman has dysuria and frequency a few days after her honeymoon. Urine culture grows Gram-positive cocci in clusters that are catalase-positive and coagulase-negative. Which test best identifies the likely species?

AA positive tube coagulase testBResistance to novobiocinCSensitivity to optochinDSensitivity to novobiocin

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

The answer and the reasoning

B. Resistance to novobiocin

Staphylococcus saprophyticus is the second commonest cause of uncomplicated cystitis in young sexually active women, and it is the coagulase-negative staphylococcus that is resistant to novobiocin. S. epidermidis, the common skin contaminant and biofilm former on prosthetic devices, is novobiocin-sensitive.

Option by option

A. A positive tube coagulase test
A positive tube coagulase identifies Staphylococcus aureus, but the isolate is coagulase-negative.
B. Resistance to novobiocin (correct)
Correct. Novobiocin resistance separates S. saprophyticus from other coagulase-negative staphylococci.
C. Sensitivity to optochin
Optochin sensitivity identifies Streptococcus pneumoniae, which is catalase-negative.
D. Sensitivity to novobiocin
Novobiocin sensitivity characterises S. epidermidis.

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 B, Resistance to novobiocin. Staphylococcus saprophyticus is the second commonest cause of uncomplicated cystitis in young sexually active women, and it is the coagulase-negative staphylococcus that is resistant to novobiocin.

Why is "A positive tube coagulase test" not the answer?

A positive tube coagulase identifies Staphylococcus aureus, but the isolate is coagulase-negative.

Why is "Sensitivity to optochin" not the answer?

Optochin sensitivity identifies Streptococcus pneumoniae, which is catalase-negative.

Why is "Sensitivity to novobiocin" not the answer?

Novobiocin sensitivity characterises S. epidermidis.

What concept does this question test?

It tests Bacteriology: Staphylococcus saprophyticus in Microbiology. S. epidermidis, the common skin contaminant and biofilm former on prosthetic devices, is novobiocin-sensitive.

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: Staphylococcus saprophyticus?

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.