Source : Webster's Revised Unabridged Dictionary (1913)

Microbe \Mi"crobe\, Microbion \Mi*cro"bi*on\, n. [NL. microbion,
   fr. Gr. ? little + ? life.] (Biol.)
   A microscopic organism; -- particularly applied to bacteria
   and especially to pathogenic forms; as, the microbe of fowl
   cholera.

Source : WordNet®

microbe
     n : a minute life form (especially a disease-causing bacterium);
         the term is not in technical use [syn: {bug}, {germ}]