English: Electron micrograph of a flagellated Listeria monocytogenes bacterium, Magnified 41,250X. Listeria monocytogenes is the infectious agent responsible for the food borne illness Listeriosis. In the United States, an estimated 2,500 persons become seriously ill with listeriosis each year. Of these, 500 die. Typical size of Listeria: rods 0.4 by 1 to 1.5 µm