**Core Concept:** Pseudomembranous colitis is a complication of Clostridium difficile infection, commonly known as C. difficile infection. It is a potentially life-threatening condition that can occur in patients who have been treated with antibiotics, particularly those affecting the gut microbiome.

**Why the Correct Answer is Right:** C. difficile infection is caused by the overgrowth of the bacterium Clostridium difficile in the gut, particularly in patients who have been treated with antibiotics that disrupt the normal balance of gut microbiota. The antibiotics eliminate beneficial bacteria, which in turn allows C. difficile to thrive and produce toxins that cause inflammation in the large intestine, leading to pseudomembranous colitis.

**Why Each Wrong Option is Incorrect:**

A. Penicillin (Option A) is not a common antibiotic that causes C. difficile infection or pseudomembranous colitis, unlike amoxicillin (Option D).

B. Penicillin (Option B) is not a common antibiotic that causes C. difficile infection or pseudomembranous colitis, unlike amoxicillin (Option D).

C. Penicillin (Option C) is not a common antibiotic that causes C. difficile infection or pseudomembranous colitis, unlike amoxicillin (Option D).

D. Amoxicillin (Option D) is a penicillin-type antibiotic that can disrupt the gut microbiota, leading to the overgrowth of C. difficile and subsequent development of pseudomembranous colitis.

**Clinical Pearl:** The key to preventing pseudomembranous colitis is to minimize the use of antibiotics, especially broad-spectrum ones, and to ensure a healthy gut microbiome through probiotics, prebiotics, and maintaining a balanced diet.

**Correct Answer:** D. Amoxicillin (Option D) is a penicillin-type antibiotic that can disrupt the gut microbiota, leading to the overgrowth of Clostridium difficile and subsequent development of pseudomembranous colitis.