pathogen vs microorganism

pathogen and microorganism both are nouns.

Word	Noun	Adjective	Verb	Adverb
pathogen	Yes	No	No	No
microorganism	Yes	No	No	No

As nouns, microorganism is a hypernym of pathogen; that is, microorganism is a word with a broader meaning than pathogen:

pathogen: any disease-producing agent (especially a virus or bacterium or other microorganism)
microorganism: any organism of microscopic size

Other hypernyms of pathogen include micro-organism, infectious agent, infective agent.

pathogen (noun)	microorganism (noun)
any disease-producing agent (especially a virus or bacterium or other microorganism)	any organism of microscopic size