False colour scanning electron micrograph (SEM) of a colony of Listeria sp., a genus of aerobic, non- sporing, Gram-positive bacteria. L. monocytogenes causes disease in man, usually meningitis or septicaemia, which affects neonates (premature babies), the elderly, chronically sick, or persons taking immuno suppressive 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 (Beta-lactamines) and gentamicin. Magnification: X 12,000 at 35mm size.