Enterohepatic Helicobacter spp. (EHS) infections are endemic in the majority of research mouse colonies. Helicobacter (H.) species (spp.) are Gram-negative, microaerophilic, spiral-to-curve-shaped bacteria with sheathed flagella. These bacteria are common colonizers of the gastrointestinal tract. Some species are associated with chronic gastrointestinal diseases in both humans and animals. Species of Helicobacter have been identified in gastrointestinal tracts of mice. These Helicobacter spp. primarily colonize the lower intestinal tract but also they have been found in the liver and bile of mice.