Shigella sp. bacterium. Coloured scanning electron micrograph (SEM) of a Shigella sp. bacterium (orange) infront of a crenated (spiked) human red blood cell (blue), known as an echinocyte. Shigella sp. are Gram-negative rod-shaped bacteria. They infect the large intestine, causing dysentery, which can vary in severity from a mild attack of diarrhoea to an acute infection. Dysentery is spread by flies, direct contact and faeces-contaminated water. Treatment is with sulphonamide drugs. Red blood cells are usually biconcave, however this cell has been exposed to a concentrated solution, causing it to shrink and change of shape. Magnification: x9,500 when printed 10 centimetres wide.