**Core Concept**
Pseudomembranous colitis, also known as Clostridioides difficile (C. difficile) infection, is a type of colitis caused by an imbalance of the gut microbiota, leading to the overgrowth of pathogenic bacteria.

**Why the Correct Answer is Right**
C. difficile is a gram-positive, spore-forming bacterium that produces toxins A and B, which damage the colonic mucosa and cause the characteristic pseudomembranes. The infection typically occurs after the use of broad-spectrum antibiotics, which disrupt the normal gut flora. The toxins produced by C. difficile cause inflammation, fluid loss, and tissue damage in the colon.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because Escherichia coli (E. coli) is a common cause of urinary tract infections, not pseudomembranous colitis.
**Option B:** This option is incorrect because Salmonella species can cause gastroenteritis, but they are not typically associated with pseudomembranous colitis.
**Option C:** This option is incorrect because Campylobacter species can cause gastroenteritis, but they are not typically associated with pseudomembranous colitis.

**Clinical Pearl / High-Yield Fact**
C. difficile infection is often associated with recent hospitalization, antibiotic use, and the use of proton pump inhibitors (PPIs). It's essential to consider C. difficile infection in patients with diarrhea, especially those with a history of recent antibiotic use.

**Correct Answer: C. Clostridioides difficile.**