**Core Concept**
_Campylobacter jejuni_ is a Gram-negative, spiral-shaped bacterium that is a leading cause of bacterial gastroenteritis worldwide. Its pathogenicity is attributed to its ability to invade the intestinal epithelial cells and cause a strong inflammatory response.

**Why the Correct Answer is Right**
_C. jejuni_ invades the intestinal epithelial cells by using its flagella to adhere to the microvilli and then using its type III secretion system to inject effector proteins that disrupt the host cell's cytoskeleton and allow the bacterium to enter the cell. This invasion is facilitated by the expression of the _cadF_ gene, which encodes a surface protein that helps the bacterium to adhere to the host cells. The inflammatory response triggered by _C. jejuni_ is characterized by the production of pro-inflammatory cytokines, such as IL-8, which attracts neutrophils to the site of infection.

**Why Each Wrong Option is Incorrect**
- **Option A:** This option is incorrect because it does not specify the correct mechanism of invasion.
- **Option B:** This option is incorrect because it does not mention the role of the _cadF_ gene in adhesion.

**Clinical Pearl / High-Yield Fact**
_C. jejuni_ infection is often associated with the Guillain-Barré syndrome, a rare autoimmune disorder that occurs when the immune system mistakenly attacks the peripheral nerves, leading to muscle weakness and paralysis.

**Correct Answer: A.