Microbes are the unicellular microscopic organism that can only be visible under the microscope. The most common types are bacteria, viruses and fungi. They exist in its single-celled form or a colony of cells. They are widespread in nature and are beneficial to life, but some can cause serious harm. The study of microorganism is known as Microbiology.

Prions are the misfolded proteins that act as an infectious agent. They have the ability to transmit their misfolded shape into normal variants of the same protein. They cause many fatal and transmissible neurodegenerative diseases. It's mode of action is very different to bacteria. They involve a protein-only infectious agent that propagates the disease by transmitting protein conformational changes. The disease results from extensive and progressive brain degeneration.