Helicobacter spp. are gram-negative bacteria that vary in their morphology, growth requirements, biochemical profiles, antibiotic susceptibility, and sequence of conserved 16S rRNA genes. Several Helicobacter spp. (H. pylori, H. hepaticus, H. bilis, H. muridarum) are urease-positive, that is, capable of producing ammonia to neutralize gastric acid, whereas others (for example H. ganmani, H. rodentium, H. trogontum, H. typhlonius, and others) are urease-negative. The Helicobacter species associated with clinical disease in rodents are primarily H. hepaticus and H. bilis.