| Bacterium | Any of a large group of microscopic organisms having round, rod-shaped, spiral, or filamentous unicellular or noncellular bodies that are often aggregated into colonies, are enclosed by a cell wall or membrane (prokaryotes), and lack fully differentiated nuclei. Bacteria range in size from 0.4µm to 2.0µm and may exist as free-living organisms in soil, water, organic matter, or as parasites in the live bodies of plants. Some are disease producing, but most perform necessary functions such as digestion, fermentation, and nitrification. Most of the forms are variously grouped under generic names such as: Alcaligenes, Dialister, Escherichia, Klebsiella, Kurthia, Pasteurella, Salmonella, and Shigella. |
