What is an example of a cellular pathogen?

A cellular pathogen is defined as a living organism that can cause disease by multiplying within a host. Bacteria, being single-celled microorganisms, fall under this category. They have a prokaryotic cellular structure, which means they are composed of cells that lack a nucleus and other membrane-bound organelles. Bacteria can invade host tissues, reproduce, and produce substances that may lead to disease symptoms.

In contrast, viruses are acellular entities that cannot reproduce independently and rely on a host's cellular machinery to replicate, making them fundamentally different from cellular pathogens. Prions, which are misfolded proteins, cause disease by inducing abnormal folding of normal cellular proteins but are not cells themselves. Non-antigenic proteins do not typically trigger an immune response as pathogens do and do not have the characteristics of infectious agents. Thus, bacteria are the clear example of a cellular pathogen in this context.