Neutrophils and Shigella bacteria. Coloured scanning electron micrograph (SEM) of neutrophil white blood cells (large, yellowgreen) and Shigella bacteria (orange, upper right). The neutrophils, as part of the bodys immune response, are extruding extracellular traps to engulf (phagocytose) and destroy the bacteria. Shigella is a Gramnegative rodshaped bacterium. It infects the large intestine and causes mild to severe forms of dysentery.