microbe vs microorganism

microbe and microorganism both are nouns.

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

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

microbe: a minute life form (especially a disease-causing bacterium); the term is not in technical use
microorganism: any organism of microscopic size

Other hypernyms of microbe include micro-organism.

microbe (noun)	microorganism (noun)
a minute life form (especially a disease-causing bacterium); the term is not in technical use	any organism of microscopic size