Bacteriology: Nocardia: 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: Nocardia

Sample item

A 60-year-old man on long-term prednisolone has cough, and CT shows cavitating lung nodules; MRI shows a brain abscess. Sputum shows thin, branching, beaded Gram-positive filaments that are weakly acid-fast with 1% sulphuric acid decolourisation. Which drug is the treatment of choice?

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

The answer and the reasoning

C. Trimethoprim-sulfamethoxazole

Nocardia species are aerobic, partially acid-fast, branching filamentous bacteria found in soil that cause pulmonary and brain infection in immunosuppressed patients. Sulphonamides, usually trimethoprim-sulfamethoxazole, are first line, with imipenem or amikacin added in severe or CNS disease and treatment lasting many months. Penicillin is used for Actinomyces.

Option by option

  • A. Penicillin G

    Penicillin G treats Actinomyces, which is non-acid-fast and anaerobic.

  • B. Amphotericin B

    Amphotericin B treats invasive fungal infections, and the filaments here are bacterial.

  • C. Trimethoprim-sulfamethoxazole (correct)

    Correct. Cotrimoxazole is the standard first-line drug for nocardiosis.

  • D. Isoniazid, rifampicin, pyrazinamide and ethambutol

    Antituberculosis therapy treats M. tuberculosis; Nocardia is only weakly acid-fast and is not reliably treated by these drugs.

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.

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Questions about this Microbiology question

What is the answer to this Microbiology question?

The best answer is C, Trimethoprim-sulfamethoxazole. Nocardia species are aerobic, partially acid-fast, branching filamentous bacteria found in soil that cause pulmonary and brain infection in immunosuppressed patients.

Why is "Penicillin G" not the answer?

Penicillin G treats Actinomyces, which is non-acid-fast and anaerobic.

Why is "Amphotericin B" not the answer?

Amphotericin B treats invasive fungal infections, and the filaments here are bacterial.

Why is "Isoniazid, rifampicin, pyrazinamide and ethambutol" not the answer?

Antituberculosis therapy treats M. tuberculosis; Nocardia is only weakly acid-fast and is not reliably treated by these drugs.

What concept does this question test?

It tests Bacteriology: Nocardia in Microbiology. Sulphonamides, usually trimethoprim-sulfamethoxazole, are first line, with imipenem or amikacin added in severe or CNS disease and treatment lasting many months. Penicillin is used for Actinomyces.

How hard is this question?

We tag it as a multi-step question: it asks you to combine more than one idea. 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: Nocardia?

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.