A 60 year old female patient complains of diarrhoea and abdominal pain. She was on antibiotic therapy earlier which comprised of Clindamycin. She is a diabetic and is on oral hypoglycemic. Stool culture revealed gram positive motile rods. The colonoscopy is done of this patient and the typical structure is revealed. Which of the following microbe is responsible for this?

**Core Concept**
The question is testing the student's knowledge of antibiotic-associated diarrhea and the pathogen responsible for pseudomembranous colitis, a condition characterized by inflammation of the colon with the formation of pseudomembranes. The condition is often caused by an imbalance of gut flora following antibiotic therapy.

**Why the Correct Answer is Right**
The use of broad-spectrum antibiotics like Clindamycin disrupts the normal gut flora, leading to an overgrowth of Clostridioides difficile (C. difficile). C. difficile produces toxins that cause inflammation and damage to the colon, resulting in pseudomembranous colitis. The gram-positive motile rods seen in the stool culture are indicative of C. difficile. The colonoscopy findings of pseudomembranes are a classic hallmark of this condition.

**Why Each Wrong Option is Incorrect**
**Option A:** Escherichia coli (E. coli) is a gram-negative rod and is not typically associated with pseudomembranous colitis. While E. coli can cause diarrhea, it is not the primary pathogen responsible for this condition.

**Option B:** Klebsiella pneumoniae is a gram-negative rod and is not typically associated with pseudomembranous colitis. Like E. coli, it can cause diarrhea but is not the primary pathogen responsible for this condition.

**Option C:** Pseudomonas aeruginosa is a gram-negative rod and is not typically associated with pseudomembranous colitis. It is more commonly associated with respiratory infections and opportunistic infections in immunocompromised patients.

**Clinical Pearl / High-Yield Fact**
When a patient presents with diarrhea and abdominal pain after antibiotic therapy, consider the possibility of C. difficile colitis, especially if they have a history of diabetes or are taking oral hypoglycemic medications. Early diagnosis and treatment with metronidazole or vancomycin can prevent complications and improve outcomes.

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

✓ Correct Answer: A. Clostridium difficile