Bacteria and neutrophil cell. Coloured scanning electron micrograph (SEM) of Shigella sp. bacteria (yellow) on the surface of a neutrophil white blood cell. Shigella sp. are Gram-negative rod- shaped bacteria. They infect the large intestine and cause 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. Neutrophils are the most abundant white blood cell. They are very motile, entering tissues to engulf (phagocytose) and destroy invading micro-organisms.