Diphtheria is due to a
Diphtheria is an infection caused by the bacterium Corynebacterium diphtheria. Symptoms include a sore throat, fever, barking cough, a grey or white patches develop in the throat. Diphtheria is usually spread between people by direct contact or through the air. It may also be spread by the contaminated object. So, the correct answer is 'Bacterium'.