**Core Concept**
Shigella is a gram-negative, non-motile, non-spore-forming bacterium that causes shigellosis, a diarrheal disease characterized by acute inflammation of the intestinal mucosa. The pathogenesis of Shigella involves invasion of the colonic epithelium, leading to a strong inflammatory response.

**Why the Correct Answer is Right**
Shigella invades colonic epithelial cells through the action of its type III secretion system (T3SS), which delivers effector proteins that manipulate the host cell's signaling pathways. The bacteria then replicate within the host cell, leading to cell death and release of more bacteria, which spread the infection. The inflammatory response is mediated by the host's immune system, which recognizes the bacterial components as foreign.

**Why Each Wrong Option is Incorrect**
* **Option A:** This option is incorrect because Shigella is indeed a gram-negative bacterium. The gram staining property is a characteristic feature of the bacterium.
* **Option B:** This option is incorrect because Shigella is non-motile. It lacks flagella and is unable to move on its own.
* **Option C:** This option is incorrect because Shigella is non-spore-forming. It does not produce spores, which are a characteristic feature of some bacteria.

**Clinical Pearl / High-Yield Fact**
Shigellosis can be prevented by practicing good hygiene, including handwashing, especially after using the bathroom and before handling food.

**Correct Answer:** B.