**Core Concept**
Tetanus is a bacterial infection caused by Clostridium tetani, a gram-positive, spore-forming bacterium that affects the nervous system. The bacterium produces tetanospasmin, a potent neurotoxin responsible for the characteristic muscle spasms and rigidity associated with tetanus.

**Why the Correct Answer is Right**
Clostridium tetani is the causative agent of tetanus, and its spores are commonly found in soil and the gastrointestinal tracts of animals. When the spores enter the body through wounds or cuts, they germinate into vegetative cells that produce tetanospasmin. This neurotoxin disrupts neurotransmitter release, leading to muscle spasms, rigidity, and other characteristic symptoms of tetanus. The toxin specifically targets the inhibitory neurotransmitter glycine, leading to excessive excitatory neurotransmission and muscle contraction.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is not provided.
**Option B:** Incorrect, as tetanus is not caused by Corynebacterium diphtheriae, which causes diphtheria.
**Option C:** Incorrect, as tetanus is not caused by Staphylococcus aureus, which is a common cause of skin and soft tissue infections.

**Clinical Pearl / High-Yield Fact**
Tetanus is characterized by muscle rigidity, spasms, and a characteristic "risus sardonicus" facial expression. The disease is often preventable with tetanus toxoid vaccination, and prompt treatment with tetanus immunoglobulin and antibiotics can reduce the severity and mortality of tetanus.

**Correct Answer:** D. Clostridium tetani.