^BListeria monocytogenes. ^b Coloured transmission electron micrograph of ^IListeria monocytogenes^i bacteria, the causative agent of the human disease ^Blisteriosis. ^b These Gram-positive coccobacillus bacteria have a thick cell wall (blue), with capsular material seen adhering. A daughter cell is at top left. ^IListeria ^Imonocytogenes^i is contracted through contaminated food. Those vulnerable include pregnant women in which the baby may be infected; the elderly; cancer patients; and those on immunosuppressive drugs. These bacteria may also be a cause of encephalitis and purulent meningitis. Magnification: x54,000 at 6x6cm size.