Which one of the following disease is not caused by bacteria?

Common cold

The correct answer is Option (3) → Common cold 

The disease that is not caused by bacteria is Common cold. It is caused by a virus, typically a rhinovirus, not a bacterium.

The others are caused by bacteria:

• Dysentery can be caused by Shigella or Entamoeba histolytica (a protozoan, but still an infection).
• Diphtheria is caused by Corynebacterium diphtheriae.
• Plague is caused by Yersinia pestis.