False-colour transmission electron micrograph (TEM) of a colony of Listeria sp., a genus of aerobic, non-sporing, Gram-positive bacteria. The bacterium in centre of image is undergoing division by binary fission. L. monocytogenes causes disease in man, usually meningitis or septicaemia, which affects neonates (premature babies), the elderly, chronically sick, or persons taking immunosuppressive drugs. Neonatal cases arise through the asymptomatic carriage of the bacteria in the vagina by the mother. Listeria infections usually respond to treatment with ampicillin and gentamicin. Magnification: x19,000 at 6x7cm size, x9,800 at 35mm size.