**Core Concept**
Clostridium tetani is a gram-positive, rod-shaped, anaerobic bacterium that produces tetanospasmin, a potent neurotoxin responsible for the clinical manifestations of tetanus.

**Why the Correct Answer is Right**
The bacterium enters the body through wounds or cuts and produces tetanospasmin, which is then transported to the central nervous system (CNS) via the bloodstream. Tetanospasmin acts at the neuromuscular junction, where it blocks the release of neurotransmitters such as glycine and GABA, leading to muscle rigidity and spasms. The toxin also affects the presynaptic release of neurotransmitters, leading to a disinhibition of motor neurons.

**Why Each Wrong Option is Incorrect**
**Option A:** Incorrect, as Clostridium perfringens is another gram-positive, rod-shaped bacterium that produces alpha-toxin, which is responsible for gas gangrene, not tetanus.
**Option B:** Incorrect, as Escherichia coli is a gram-negative, rod-shaped bacterium that is commonly found in the human gut and is not associated with tetanus.
**Option C:** Incorrect, as Bacillus anthracis is a gram-positive, rod-shaped bacterium that produces anthrax toxin, which is responsible for anthrax, not tetanus.

**Clinical Pearl / High-Yield Fact**
Tetanus toxin is highly resistant to heat and can survive for months in the environment, making it a significant concern for wound management and infection control in healthcare settings.

**Correct Answer: C. Clostridium tetani.**