Gram-negative bacilli are responsible for numerous diseases. Some are commensal organisms present among normal intestinal flora. These commensal organisms plus others from animal or environmental reservoirs may cause disease.
Gram-negative bacteria cause plague, cholera, and typhoid fever. These infections are rare in the US but are more common in areas of the world that are affected by poverty or war or have poor sanitation and/or an unsafe water and food supply. These infections can be serious.