Neutrophil cell and bacteria. Coloured scanning electron micrograph (SEM) of bacteria (rod-shaped) and part of a neutrophil cell (lower left). The neutrophil cell (a type of white blood cell) is extruding material towards the bacteria. It may be forming a net-like structure to trap them. This is called a NET (neutrophil extracellular trap). This previously unknown method of cellular defence was discovered in 2004. These are Shigella sp. bacteria, one of the causes of dysentery, a severe intestinal inflammation.