Bacteriology: staphylococcal exfoliative toxin: 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: staphylococcal exfoliative toxin

Sample item

A 10-day-old neonate has fever, perioral erythema and flaccid blisters that rupture to leave moist red skin. Gentle rubbing produces skin separation, the mouth is spared, and blister fluid is sterile on culture. Which molecular event explains the lesions?

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

The answer and the reasoning

B. Cleavage of desmoglein-1 in the stratum granulosum by a staphylococcal serine protease

This is staphylococcal scalded skin syndrome. Phage group II Staphylococcus aureus produces exfoliative toxins A and B, serine proteases that cleave desmoglein-1 and split the granular layer. The toxin is carried through blood from a distant focus, so the blister fluid is sterile and mucosae are spared because they lack desmoglein-1 as the main adhesion molecule.

Option by option

  • A. Antibody attack on BP180 at the dermo-epidermal junction

    BP180 antibodies cause bullous pemphigoid with subepidermal blisters, mostly in the elderly.

  • B. Cleavage of desmoglein-1 in the stratum granulosum by a staphylococcal serine protease (correct)

    Correct. Exfoliative toxin cleaves desmoglein-1 and causes superficial epidermal splitting.

  • C. Autoantibodies against desmoglein-3 in the suprabasal layer

    Desmoglein-3 autoantibodies cause pemphigus vulgaris in adults, with mucosal erosions.

  • D. Mutation of keratin 5 and 14 in the basal layer

    Keratin mutations cause epidermolysis bullosa simplex, which is inherited and not febrile.

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, Cleavage of desmoglein-1 in the stratum granulosum by a staphylococcal serine protease. This is staphylococcal scalded skin syndrome.

Why is "Antibody attack on BP180 at the dermo-epidermal junction" not the answer?

BP180 antibodies cause bullous pemphigoid with subepidermal blisters, mostly in the elderly.

Why is "Autoantibodies against desmoglein-3 in the suprabasal layer" not the answer?

Desmoglein-3 autoantibodies cause pemphigus vulgaris in adults, with mucosal erosions.

Why is "Mutation of keratin 5 and 14 in the basal layer" not the answer?

Keratin mutations cause epidermolysis bullosa simplex, which is inherited and not febrile.

What concept does this question test?

It tests Bacteriology: staphylococcal exfoliative toxin in Microbiology. Phage group II Staphylococcus aureus produces exfoliative toxins A and B, serine proteases that cleave desmoglein-1 and split the granular layer. The toxin is carried through blood from a distant focus, so the blister fluid is sterile and mucosae are spared because they lack desmoglein-1 as the main adhesion molecule.

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: staphylococcal exfoliative toxin?

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.