**Core Concept**
Flask-shaped ulcers in the sigmoid colon are a hallmark of *Clostridioides difficile* infection (CDI), particularly in the context of lower gastrointestinal bleeding. These ulcers are characterized by a flask-like appearance due to the formation of a central necrotic core with a raised border, and are commonly seen in patients with recent antibiotic use or immune suppression.

**Why the Correct Answer is Right**
*Clostridioides difficile* infection is a leading cause of antibiotic-associated diarrhea and colitis, presenting with bloody diarrhea and sigmoid colon ulcers. Flask-shaped ulcers are pathognomonic for CDI. The most effective initial treatment for severe or complicated CDI is intravenous metronidazole, which targets *C. difficile* by disrupting its cell membrane. It is first-line in hospitalized patients with severe colitis, especially when sigmoidoscopy reveals characteristic ulcers.

**Why Each Wrong Option is Incorrect**
Option A: Ceftriaxone is a third-generation cephalosporin, used for bacterial infections like sepsis or urinary tract infections, but it does not treat *C. difficile* and may actually worsen CDI by disrupting gut flora.
Option C: Steroids and sulphasalazine are used in ulcerative colitis, not CDI. Sulphasalazine is ineffective against *C. difficile* and steroids may worsen infection.
Option D: Hydrocortisone enemas are used in acute ulcerative colitis or for localized inflammation, not in *C. difficile* infection. They do not target the causative organism.

**Clinical Pearl / High-Yield Fact**
Flask-shaped ulcers in the sigmoid colon = *Clostridioides difficile* infection. Always consider CDI in patients with diarrhea and GI bleeding after antibiotic use. Metronidazole is first-line IV therapy for severe cases.

✓ Correct Answer: B. Intravenous metronidazole