Shiga toxin is preduced by-
**Core Concept**
Shiga toxin is a potent exotoxin produced by certain strains of bacteria that causes severe damage to the endothelial cells lining the blood vessels, leading to hemorrhagic colitis and hemolytic uremic syndrome (HUS). This toxin works by inhibiting protein synthesis in host cells.
**Why the Correct Answer is Right**
The correct answer is Shigella dysenteriae type 1, which is a Gram-negative bacterium commonly associated with dysentery. Shiga toxin is encoded by the bacterium's bacteriophage genome and is produced in response to stress or nutrient limitation. The toxin binds to the glycolipid receptors on the surface of host cells, specifically globotriaosylceramide (Gb3), and enters the cell through receptor-mediated endocytosis. Once inside the cell, the toxin is cleaved into two fragments, A and B. Fragment B is responsible for binding to the host cell receptor, while fragment A is responsible for catalyzing the depurination of the 28S rRNA in the 60S subunit of the ribosome, leading to the inhibition of protein synthesis.
**Why Each Wrong Option is Incorrect**
**Option A:** E. coli is a common producer of Shiga toxin, but it is not the only bacterium that produces this toxin. While certain strains of E. coli, such as E. coli O157:H7, are known to produce Shiga toxin, the question asks for the bacterium that produces Shiga toxin in general, and Shigella dysenteriae type 1 is a more specific answer.
**Option B:** Vibrio cholerae produces cholera toxin, which causes a different type of diarrhea, and is not associated with the production of Shiga toxin.
**Option C:** Salmonella Typhi produces a different set of toxins, including Salmonella pathogenicity island 1 (SPI-1) and SPI-2, which are involved in the invasion and survival of the bacterium within host cells, but it does not produce Shiga toxin.
**Clinical Pearl / High-Yield Fact**
Shiga toxin is a classic example of an exotoxin that causes damage to the host cells through the inhibition of protein synthesis, and its production is often associated with severe gastrointestinal symptoms and complications such as HUS.
**Correct Answer: D. Shigella dysenteriae type 1**