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INI-CET EXAM -2025

Microbiology

Easy

Appeared in: INI-CET EXAM -2025

Explanation

The statement that diphtheria toxin is the most potent toxin known to man is incorrect.
The most potent biological toxin is Botulinum toxin, produced by the bacterium Clostridium botulinum.
While diphtheria toxin is highly lethal and a single molecule can kill a cell, its lethal dose is higher (meaning it is less potent) than that of Botulinum toxin.

Option A: This statement is correct. The ability of C. diphtheriae to produce toxin is dependent on it being infected by a specific bacteriophage (β-corynephage) that carries the tox gene.
Option B: This statement is correct. The diphtheria exotoxin disseminates through the bloodstream and can cause severe systemic complications, with myocarditis being one of the most serious and life-threatening.
Option C: This statement is correct. Diphtheria toxin is a classic example of an exotoxin, which is a toxin secreted by a bacterium into its surroundings.

Clinical Relevance

Nursing practice connection: This is primarily an exam-oriented knowledge point with limited direct bedside application, so retain The question tests knowledge of the characteristics and pathophysiology of the toxin produced by Corynebacterium diphtheriae as background academic context rather than a clinical decision trigger.
Recognizing the 'bull neck' sign is critical for nurses as it indicates severe diphtheria, a medical emergency requiring immediate intervention with diphtheria antitoxin and antibiotics to prevent airway obstruction and systemic complications like myocarditis.
This case underscores the vital importance of routine childhood immunization with the DTaP/Tdap vaccine, which is highly effective in preventing diphtheria.
What if the patient was fully vaccinated? While rare, diphtheria can occur in vaccinated individuals, though it is typically much milder. The presence of a 'bull neck' in a vaccinated person would be highly unusual and might suggest a different diagnosis or a particularly virulent strain.

How to Approach the Question

First, analyze the image to identify the key clinical sign. The massive neck swelling is the classic 'bull neck' appearance characteristic of severe diphtheria.
Next, understand the question's requirement. You need to find the statement that is FALSE or incorrect about diphtheria.
Evaluate each option based on your knowledge of diphtheria's pathophysiology:
Option A (Phage coded): Recall that the toxin gene is carried by a virus (bacteriophage). This is a known fact. So, this is correct.
Option B (Causes myocarditis): Recall that heart complications are a major risk in diphtheria. This is correct.
Option C (It is an exotoxin): Recall that the toxin is secreted by the bacteria, making it an exotoxin. This is correct.

Concept Tested & Keywords

Concept Tested: The question tests knowledge of the characteristics and pathophysiology of the toxin produced by Corynebacterium diphtheriae.
Stem keywords: image, incorrect, bull neck, diphtheria
Lead-in keywords: incorrect
Clinical cues: The 'bull neck' appearance is a critical visual cue pointing towards a diagnosis of severe diphtheria, indicating significant edema and lymph node enlargement.
Negative lead-in flag: The question asks for the INCORRECT statement.

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