Macrophages engulfing E. coli. Coloured scanning electron micrograph (SEM) of white blood cells (macrophages, orange) engulfing Escherichia coli bacteria (red rods). This process is called phagocytosis. E. coli bacteria are found in the lower intestines of most mammals. They are usually harmless, but different strains can cause meningitis, septicaemia or food poisoning. Macrophages attack many types of disease-causing organisms and clean up cellular debris. Magnification: x1300 when printed 10 centimetres wide.