What symptom is primarily associated with infection from Clostridium tetani?

Clostridium tetani is the bacterium responsible for tetanus, a serious condition characterized by severe muscle stiffness and spasms. The most defining symptom of tetanus is indeed muscle spasms, which occur due to the neurotoxin produced by the bacteria. This toxin interferes with the transmission of nerve impulses, leading to sustained contractions of muscles.

Muscle spasms typically start in the jaw (often described as "lockjaw") and can spread to other parts of the body. This symptom is a result of the toxin's action on the motor neurons, leading to hypertonicity and opisthotonos (spasms causing arching of the back).

Other symptoms associated with tetanus may include sweating, spontaneous erections, and difficulty swallowing, but muscle spasms remain the hallmark symptom and are critically important when diagnosing and understanding the disease. In the context of the options provided, muscle spasms stand out as the primary and most characteristic symptom of Clostridium tetani infection.