For the past week, a 65-year-old woman has been treated for a severe infection with broad-spectrum antibiotics, and she had recovered well. Over the past day, however, she has developed foul-smelling, voluminous, greenish, watery diarrhea, as well as abdominal pain and fever. She is diagnosed with pseudomembranous colitis. Which of the following is the mechanism associated with this condition?

**Core Concept**
Pseudomembranous colitis, caused by Clostridioides difficile (C. difficile), is a condition characterized by the overgrowth of pathogenic bacteria in the colon, leading to inflammation and damage to the intestinal mucosa. This condition often occurs after antibiotic therapy disrupts the normal gut flora.

**Why the Correct Answer is Right**
The mechanism behind pseudomembranous colitis involves the production of toxins by C. difficile, specifically toxin A and toxin B. Toxin A causes the formation of pseudomembranes, which are thick, white or yellowish patches of mucus and inflammatory cells. Toxin B, on the other hand, causes the disruption of the cytoskeleton of intestinal epithelial cells, leading to cell death and the release of inflammatory mediators. This results in the symptoms of diarrhea, abdominal pain, and fever.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because it refers to the mechanism of action of Clostridioides difficile toxin A, which is not the primary mechanism associated with pseudomembranous colitis.

**Option B:** This option is incorrect because it refers to the mechanism of action of Clostridioides difficile toxin B, which is one of the two primary toxins responsible for pseudomembranous colitis. However, it is not the only mechanism.

**Option C:** This option is incorrect because it refers to the mechanism of action of Clostridioides difficile toxin B, which is one of the two primary toxins responsible for pseudomembranous colitis, but it is incomplete.

**Option D:** This option is incorrect because it is not a known mechanism associated with pseudomembranous colitis.

**Clinical Pearl / High-Yield Fact**
It is essential to note that the use of broad-spectrum antibiotics can lead to the disruption of the normal gut flora, making patients more susceptible to C. difficile infection. The risk of developing pseudomembranous colitis can be reduced by using narrow-spectrum antibiotics whenever possible and using probiotics to maintain the balance of gut flora.

**Correct Answer:** C. The production of toxins by C. difficile, specifically toxin A and toxin B, is the mechanism associated with pseudomembranous colitis.

✓ Correct Answer: B. Bacterial release of exotoxin, inducing necrosis of the mucosa