Yersinia enterocolitica using Gram-stain technique. Yersinia enterocolitica is a Gram-negative bacillus-shaped bacterium, belonging to the family Enterobacteriaceae. Yersinia enterocolitica infection causes the disease yersiniosis, which is an animal-borne disease occurring in humans, as well as in a wide array of animals such as cattle, deer, pigs, and birds. Many of these animals recover from the disease and become carriers; these are potential sources of contagion despite showing no signs of disease. Symptoms of yersiniosis are fever, abdominal pain, and diarrhea (often bloody), and Yersinia enterocolitica is the cause of most yersinia-related illnesses in the U.S. (mostly in children).