**Core Concept**
Clostridium tetani is a Gram-positive, anaerobic, rod-shaped bacterium that produces a potent neurotoxin, tetanospasmin. This toxin causes the characteristic symptoms of tetanus, including muscle rigidity, spasms, and rigidity of the jaw, which is known as lockjaw.

**Why the Correct Answer is Right**
Tetanospasmin acts by blocking the release of neurotransmitters, such as glycine and GABA, which are inhibitory neurotransmitters in the spinal cord. This leads to an increase in the excitability of motor neurons, resulting in muscle spasms and rigidity. The toxin also affects the release of neurotransmitters in the autonomic nervous system, leading to symptoms such as hypertension and tachycardia.

**Why Each Wrong Option is Incorrect**
**Option A:** Incorrect because Clostridium tetani is indeed a Gram-positive bacterium, and its anaerobic nature is a key factor in its pathogenesis.
**Option B:** Incorrect because tetanospasmin is a potent neurotoxin that is responsible for the symptoms of tetanus, not a bacteriotoxin that kills bacteria.
**Option C:** Incorrect because Clostridium tetani is typically found in soil, dust, and the gastrointestinal tracts of animals, and is often introduced into the body through wounds or puncture wounds.

**Clinical Pearl / High-Yield Fact**
Tetanus infection is often prevented by vaccination with tetanus toxoid, which is a toxoid that is inactivated by heat and is therefore non-toxic. However, the toxoid still stimulates an immune response that produces antibodies against tetanospasmin.

**Correct Answer:** A