Listeria monocytogenes. Coloured transmission electron micrograph of the bacteria Listeria monocytogenes, causative agent of listeriosis" in humans. These Gram-positive, soil saprophytic bacteria have a thick cell wall (brown), with capsular material seen adhering. It is contracted through contaminated food. Pregnant women are especially vulnerable; bacteria may cross the placenta to infect the baby which has no immunity. The elderly, cancer patients and those on immunosuppressive drugs are also vulnerable. These bacteria may be a cause of encephalitis & purulent meningitis. Magnification: x83,000 at 6x4.5cm size."