Yersinia enterocolitica bacteria, 3D computer illustration based on scanning electron microscopy (SEM) imagery. This is a Gram- negative, rod-shaped bacterium that is found in soil, water and the intestinal tracts of animals. In humans the consumption of undercooked meat (most often pork) or water contaminated with Y. enterocolitica causes enteritis, an inflammation of the small intestines accompanied by fever, abdominal pain and diarrhoea.