Which test(s) are based on the principle of toxin neutralization in medical microbiology?
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ANagler’s reaction for Clostridium perfringens alpha-toxin
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BSchick test for diphtheria immunity
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CBoth (a) and (b)
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DNone of these
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EWidal test for enteric fever agglutinins
Answer
Correct Answer: Both (a) and (b)
Explanation
Introduction / Context:Toxin neutralization assays assess whether specific antibodies can inhibit the biological activity of a bacterial toxin. Two classic examples are Nagler’s reaction (plate-based antitoxin neutralization of lecithinase) and the Schick test (intradermal diphtheria toxin challenge neutralized by preexisting antitoxin).
Given Data / Assumptions:
- Nagler’s reaction: colony lecithinase halo is abolished adjacent to antitoxin.
- Schick test: a negative skin reaction indicates circulating antitoxin that neutralizes the diphtheria toxin dose.
Concept / Approach:Neutralization occurs when antibodies bind toxin epitopes, blocking enzymatic or receptor-binding steps. In plates (Nagler), antitoxin diffuses and prevents opaque precipitation of digested lecithin. In vivo (Schick), toxin elicits erythema if not neutralized; prior immunity yields no lesion.
Step-by-Step Solution:
1) Identify tests that rely on antitoxin abolishing toxin effects.2) Map Nagler and Schick to that principle.3) Select “Both (a) and (b).”Verification / Alternative check:Standard references describe both tests as demonstrations of functional neutralization by specific antitoxins.
Why Other Options Are Wrong:
- Widal: Agglutination test for Salmonella antibodies, not toxin neutralization.
- “None”: contradicted by the well-known mechanisms of Nagler and Schick tests.
Common Pitfalls:
- Confusing agglutination or precipitation assays (antigen–antibody lattice) with true functional neutralization tests.
Final Answer:Both (a) and (b)