**Question:** All of the following are true about Helicobacter pylori except -

A. Helicobacter pylori is a Gram-negative bacterium
B. It is a causative agent for peptic ulcer disease
C. It is a common cause of gastritis
D. It is primarily found in the small intestine

**Core Concept:**
Helicobacter pylori (H. pylori) is a Gram-negative bacterium that is commonly associated with various gastrointestinal diseases, including gastritis, peptic ulcer disease, and gastric cancer. While H. pylori is indeed a causative agent for peptic ulcer disease and gastritis, it is not primarily found in the small intestine. Instead, it is commonly localized within the gastric mucosa of the human stomach.

**Why the Correct Answer is Right:**
D. H. pylori is primarily found in the small intestine (Option D) is incorrect because the bacterium is primarily localized in the gastric mucosa of the human stomach. This misconception may stem from the fact that H. pylori can occasionally be found in the small intestine, but it is not its primary habitat.

**Why Each Wrong Option is Incorrect:**
A. Although H. pylori is a Gram-negative bacterium (Option A), the misconception lies in its primary location within the stomach, not the small intestine.
B. H. pylori is a known causative agent for peptic ulcer disease (Option B) and gastritis (Option C); however, its primary location is still within the stomach, making Option D incorrect.

**Clinical Pearl:**
A better understanding of H. pylori biology and its primary location within the stomach can help healthcare professionals accurately diagnose, treat, and manage patients with associated gastrointestinal disorders, such as peptic ulcers and gastritis, in a more effective manner.