The relationship between bacteria and a host where the bacteria causes harm is called parasitism.

Here's why:

* Parasitism is a relationship where one organism (the parasite) benefits at the expense of another organism (the host).

* Bacteria can act as parasites by causing disease or harm to the host.

Examples of parasitic bacteria include:

* Salmonella causing food poisoning

* Staphylococcus aureus causing skin infections

* Mycobacterium tuberculosis causing tuberculosis

It's important to note that not all bacteria are harmful. Many bacteria are beneficial or even essential for human health.