and

and are Gram-negative microaerophilic bacteria that are widely distributed in the animal kingdom. They have been known as animal pathogens for nearly 100 years. However, because they are fastidious and slow-growing in culture, they have been recognized as human gastrointestinal pathogens only during the last 20 years. They can cause diarrheal illnesses, systemic infection, chronic superficial gastritis, peptic ulcer disease, and can lead to gastric carcinoma. Table 23-1 lists the species known to be pathogenic for humans. , and, less often, and are the most common bacterial causes of acute diarrheal illnesses in developed countries. (formerly known as ), which was first cultured from gastric biopsy tissues in 1982, causes chronic superficial gastritis and is associated with the pathogenesis of peptic ulcer disease and gastric cancer. subspecies occasionally causes systemic illnesses in compromised hosts.