Any minute living organism, particularly one capable of causing disease; viruses, because they are not living organisms, technically are not considered "microbes," but are more correctly referred to by a term such as "infectious agent."
Microbe (Zachary Smith Jr.) is a fictional character, a superhero from Marvel Comics. He debuted in New Warriors Vol. 3 #1. He is a mutant with the ability to communicate with germs and other microscopic organisms.