What is an example of a microorganism acting in a harmful way?

Microorganisms present in our body Re viruses, bacteria, fungi, algae, and protozoa among which most of them cause immense benefits to the body. There are some harmful microorganisms too known as pathogens which cause disease and cause a threat to all existing life forms of the earth which can result in death at times.

Explanation:

bacteries making us sick or forming developing

it would be a gas formation