True about diphtheria is –
**Core Concept**
Diphtheria is a bacterial infection caused by Corynebacterium diphtheriae, characterized by the formation of a thick, gray membrane in the throat. This membrane is a result of the toxin produced by the bacteria, which interferes with the normal functioning of the respiratory epithelium.
**Why the Correct Answer is Right**
The toxin, known as diphtheria toxin, works by inhibiting the protein synthesis in cells by inactivating the elongation factor-2 (EF-2). This leads to cell death and the formation of the characteristic membrane. The toxin also causes systemic toxicity, including cardiac and neurological manifestations. The toxin is produced by the bacteria in response to the host's immune response, and its production is regulated by the bacterium's genetic material.
**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because it does not specify the toxin's mechanism of action, which is crucial for understanding the pathophysiology of diphtheria.
**Option B:** This option is incorrect because it does not mention the bacterium responsible for the infection, which is a fundamental aspect of diphtheria.
**Option C:** This option is incorrect because it does not accurately describe the toxin's mechanism of action, which involves the inhibition of protein synthesis.
**Clinical Pearl / High-Yield Fact**
Diphtheria toxin is a classic example of a bacterial exotoxin, which is a potent and highly toxic substance produced by bacteria. The toxin's mechanism of action, involving the inhibition of protein synthesis, is a key aspect of its pathophysiology.
**Correct Answer: D.**