Clinical microbiology and hospital infection control: Serratia outbreak: 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 · Clinical microbiology and hospital infection control: Serratia outbreak

Sample item

Several ICU patients develop urinary and respiratory infections with a Gram-negative bacillus that forms red-pigmented colonies at room temperature. Cultures trace the source to a contaminated liquid soap dispenser. Which organism is it?

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

The answer and the reasoning

B. Serratia marcescens

Serratia marcescens produces a red pigment, prodigiosin, especially at room temperature, and is a recognised cause of hospital outbreaks from contaminated solutions and equipment. It is intrinsically resistant to several antibiotics.

Option by option

  • A. Chromobacterium violaceum

    Chromobacterium violaceum produces a violet pigment and is a tropical soil organism.

  • B. Serratia marcescens (correct)

    Correct. Red-pigmented colonies and hospital outbreaks from contaminated fluids suggest Serratia.

  • C. Proteus mirabilis

    Proteus mirabilis swarms on agar and is urease positive, without red pigment.

  • D. Pseudomonas aeruginosa

    Pseudomonas aeruginosa produces green-blue pyocyanin and a grape-like smell.

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 B, Serratia marcescens. Serratia marcescens produces a red pigment, prodigiosin, especially at room temperature, and is a recognised cause of hospital outbreaks from contaminated solutions and equipment.

Why is "Chromobacterium violaceum" not the answer?

Chromobacterium violaceum produces a violet pigment and is a tropical soil organism.

Why is "Proteus mirabilis" not the answer?

Proteus mirabilis swarms on agar and is urease positive, without red pigment.

Why is "Pseudomonas aeruginosa" not the answer?

Pseudomonas aeruginosa produces green-blue pyocyanin and a grape-like smell.

What concept does this question test?

It tests Clinical microbiology and hospital infection control: Serratia outbreak in Microbiology. It is intrinsically resistant to several 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 Clinical microbiology and hospital infection control: Serratia outbreak?

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.