No exact answer is possible. Certainly many thousands
Virus is most harmful
poison
There are many products of an organism that destroys or weakens harmful microorganisms. This could be an enzyme for example.
Type your answer here... What is useful of a microorganism
One harmful effect is dying or diesease
Tonsils
tintre
Bacteria infecting a cut.
Microorganism are sometimes only harmful in certain environment. Some organisms that may be harmful to some people or animals may not be harmful to others.
Protists - a mixed group of single and many celled organisims of all types.
microorganisms can be harmful and useful! Yeast is a microorganism and is used in bread. but some bacteria (microorganism) can be harmful, they can make you ill or kill you. but in our imune system there are antibacteria fighting off disease and protecting us. So microorganisms can be harmful and beneficial
Mould eats potentially harmful microorganism, though, as it is itself harmful, eating it isn't recommended. FYI- Penicillin is a form of bread mold.