False colour scanning electron micrograph of the rodshaped bacteria Yersinia enterocolitica (gram negative), an enterobacteria. Y.enterocolitica may cause enteritis an inflammation of the small intestines, accompanied by abdominal pain, fever, vomiting and diarrhoea. It is thought to be a food poisoning organism. Although it has been isolated from a variety of food, none of the strains were associated with human infection. As of 1987, the pig appeared to be the only animal species to harbour the pathogenic human strain and it was uncertain whether it was an important source of human infection. Magnification: x1690 at 35mm size.