**Core Concept**
Granulomatous amoebic encephalitis is a rare and serious infection of the brain caused by free-living amoebas. The underlying principle being tested is the ability to identify the causative agent of this condition, which is typically an amoeba that infects the brain and central nervous system.

**Why the Correct Answer is Right**
The correct answer is Acanthamoeba, which is a type of free-living amoeba that can cause granulomatous amoebic encephalitis. This condition occurs when the amoeba infects the brain, leading to a severe and potentially life-threatening infection.

**Why Each Wrong Option is Incorrect**
**Option B:** Incorrect because Naegleria fowleri causes primary amoebic meningoencephalitis, a different condition.
**Option C:** Incorrect because Entamoeba histolytica primarily causes intestinal infections.
**Option D:** Incorrect because Toxoplasma gondii causes toxoplasmosis, which is a different type of infection.

**Clinical Pearl / High-Yield Fact**
Granulomatous amoebic encephalitis is a rare but serious condition that requires prompt diagnosis and treatment. Acanthamoeba infection is often associated with contact lens use or exposure to contaminated water.

**Correct Answer:** A. Acanthamoeba