- A very tiny form of life — microbes include bacteria, fungi, and protozoan parasites — best visualized with a microscope. The word "microbe" did not enter English usage until 1881. It was put together from Greek roots "mikros," small + "bios," life = small (form of) life.
* * *Any very minute organism. As originated, the word was intended as a collective term for the large variety of microorganisms then known in the 19th century; modern usage has retained the original collective meaning but expanded it to include both microscopic and ultramicroscopic organisms (spirochetes, bacteria, rickettsiae, and viruses). These organisms are considered to form a biologically distinctive group, in that the genetic material is not surrounded by a nuclear membrane, and mitosis does not occur during replication. [Fr., fr. G. mikros, small, + bios, life]
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* * *n.
* * *mi·crobe (miґkrōb) [micro- + Gr. bios life] microorganism. 2. sometimes restricted to microorganisms that cause disease.
Medical dictionary. 2011.