CNRI / SCIENCE PHOTO LIBRARY CNRI / SCIENCE PHOTO LIBRARY
False colour scanning electron micrograph (SEM) of a colony of Yersinia pestis, a species of gram- negative, non-motile, capsulated bacilli (oval/rod-shaped bacteria) that is the causative agent of bubonic plague (the Black Death of the Middle Ages). The bacteria is primarily a flea- carried pathogen of rats. Transfer to man occurs when a flea is obliged to leave its dead rodent host (often because its feeding apparatus is blocked by multiplying bacteria and it is starving) and suck human blood. Infection is rapid, featuring swelling (bubo) of lymph nodes and leading to septicaemia and pulmonary infection. Magnification: X 1,200 at 35mm size.
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