Here's a breakdown:

* Viruses: These are tiny infectious agents that can only replicate inside the living cells of a host organism. They are not considered living organisms because they cannot reproduce on their own. Examples include the influenza virus, HIV, and the common cold virus.

* Bacteria: These are single-celled organisms that can exist independently of host cells. While many bacteria are beneficial, some are pathogenic and can cause disease. Examples include E. coli, Salmonella, and Staphylococcus.

While viruses and bacteria are both pathogens, they differ in how they invade and interact with body cells:

* Viruses: Viruses invade cells and hijack their machinery to replicate themselves.

* Bacteria: Bacteria can either invade cells or produce toxins that damage cells from outside.

It's important to note that some fungi, parasites, and prions can also be considered pathogens.