Bacteriology: 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

Sample item

A chronic alcoholic has rusty sputum and lobar consolidation. Sputum Gram stain shows lancet-shaped Gram-positive diplococci with alpha-haemolytic colonies. Which test best separates the organism from viridans streptococci?

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

The answer and the reasoning

D. Optochin sensitivity

This is Streptococcus pneumoniae, which is optochin sensitive and bile soluble, whereas viridans streptococci are optochin resistant and bile insoluble. Both are catalase negative, so the catalase test cannot separate them.

Option by option

  • A. Bacitracin sensitivity

    Bacitracin sensitivity identifies Group A streptococci (Streptococcus pyogenes).

  • B. Catalase test

    Both are catalase negative, so catalase testing does not distinguish them from each other.

  • C. Coagulase test

    Coagulase differentiates Staphylococcus aureus from other staphylococci and does not apply to streptococci.

  • D. Optochin sensitivity (correct)

    Correct. Pneumococci are inhibited by optochin, while viridans streptococci are not.

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.

More Microbiology questions

Questions about this Microbiology question

What is the answer to this Microbiology question?

The best answer is D, Optochin sensitivity. This is Streptococcus pneumoniae, which is optochin sensitive and bile soluble, whereas viridans streptococci are optochin resistant and bile insoluble.

Why is "Bacitracin sensitivity" not the answer?

Bacitracin sensitivity identifies Group A streptococci (Streptococcus pyogenes).

Why is "Catalase test" not the answer?

Both are catalase negative, so catalase testing does not distinguish them from each other.

Why is "Coagulase test" not the answer?

Coagulase differentiates Staphylococcus aureus from other staphylococci and does not apply to streptococci.

What concept does this question test?

It tests Bacteriology in Microbiology. Both are catalase negative, so the catalase test cannot separate them.

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?

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.