**Core Concept**
Pseudomembranous colitis, also known as Clostridioides difficile (C. difficile) colitis, is a type of colitis caused by an overgrowth of the bacterium Clostridioides difficile in the colon. This condition often occurs after the use of broad-spectrum antibiotics, which disrupt the normal balance of gut flora.

**Why the Correct Answer is Right**
The correct answer is related to the pathophysiology of pseudomembranous colitis. C. difficile produces toxins A and B, which cause inflammation and damage to the colonic mucosa, leading to the characteristic pseudomembranes. The pseudomembranes are composed of fibrin, leukocytes, and bacteria, which form a layer on the surface of the colonic mucosa. This process disrupts the normal barrier function of the gut and leads to the clinical manifestations of pseudomembranous colitis.

**Why Each Wrong Option is Incorrect**
**Option A:**
* This option is incorrect because pseudomembranous colitis is indeed characterized by the presence of pseudomembranes, which are a hallmark of the condition.

**Option B:**
* This option is incorrect because pseudomembranous colitis is a known complication of antibiotic use, particularly broad-spectrum antibiotics.

**Option C:**
* This option is incorrect because pseudomembranous colitis is a type of colitis that affects the colon, rather than the small intestine.

**Option D:**
* This option is incorrect because pseudomembranous colitis is indeed caused by the overgrowth of C. difficile, which produces toxins A and B.

**Clinical Pearl / High-Yield Fact**
To remember the key features of pseudomembranous colitis, recall the acronym "C. diff-icult": C (colon), diff (difficult), andicult (inflammation). This will help you associate the condition with the characteristic pseudomembranes and the overgrowth of C. difficile.

**Correct Answer:** D.