The correct option is
A Bacterium
Tetanus is an infection caused by bacteria
Clostridium tetani. It is characterized by the painful muscle spasms. It affects the nervous system of the body. The symptoms include difficulty swallowing, stiffness in jaw muscles, neck muscles, abdominal muscles. The bacterial spore is present in soil, saliva, dust, manure.
Thus, the correct answer is 'Bacterium.'