Bacteriology: anaerobes: 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: anaerobes

Sample item

A patient after colorectal surgery develops a pelvic abscess. Culture yields a bile-resistant, Gram-negative anaerobic bacillus. Which drug gives best anaerobic cover?

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

The answer and the reasoning

B. Metronidazole

Bacteroides fragilis is the commonest anaerobe in intra-abdominal abscess and is reliably treated with metronidazole. Aminoglycosides need oxygen for uptake and are inactive against anaerobes.

Option by option

  • A. Ciprofloxacin

    Ciprofloxacin has poor anaerobic activity.

  • B. Metronidazole (correct)

    Correct. Metronidazole is active against Bacteroides.

  • C. Trimethoprim-sulfamethoxazole

    Cotrimoxazole is unreliable against Bacteroides.

  • D. Gentamicin

    Aminoglycosides do not work against anaerobes.

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 B, Metronidazole. Bacteroides fragilis is the commonest anaerobe in intra-abdominal abscess and is reliably treated with metronidazole.

Why is "Ciprofloxacin" not the answer?

Ciprofloxacin has poor anaerobic activity.

Why is "Trimethoprim-sulfamethoxazole" not the answer?

Cotrimoxazole is unreliable against Bacteroides.

Why is "Gentamicin" not the answer?

Aminoglycosides do not work against anaerobes.

What concept does this question test?

It tests Bacteriology: anaerobes in Microbiology. Aminoglycosides need oxygen for uptake and are inactive against anaerobes.

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: anaerobes?

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.