How is bacteria used in medicine?

http://en.wikipedia.org/wiki/List_of_clinically_important_bacteria

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There are many bacterias that are important for medical uses.

Some have even been used for bacteriological warfare.

however.

For a bacteria to be of use in medicine, it need to have some sort of property we want.

A bacteria is normally dangerous for humans when it rapidly multiply and produces toxins. In order to produce toxins and multiply it eats away on us.

Some of the toxins a bacteria produces can actually be of help an the specific bacterias for that are cultivated in a nourishing mixture and the toxins are distilled out.

These toxins can be put in medicine afterwards and can help to cure various illnesses, even kill off other germs we don't want in our systems.

Bacteria can also be "killed off" or "disabled" and injected into our bodies to form an response from our immune system. This is done in various Vaccines. When the body afterwards encounter the real thing, it already know what the bacteria looks like and kills it off swiftly so that we don't get ill (or as ill as we could have become)

A general answer for a general question but I you out.

Regards.