The causative agent of typhoid fever is the bacterium Salmonella typhi. (Image courtesy of the Centers for Disease Control and Prevention.)

This picture shows the organism Yersinia enterocolitica. Yersinia organisms cause a wide range of disease but are most often associated with diarrhea or gastrointestinal symptoms. Yersinia infection is appearing with increased frequency in immunocompromised individuals. (Image courtesy of the Centers for Disease Control and Prevention.)

Campylobacter jejuni infection causes cramping, diarrhea, abdominal pain and fever within 2 to 5 days after a person has been exposed to the organism. Campylobacter jejuni is one of the most common bacterial causes of diarrhea. Most cases of Campylobacter jejuni come from handling or ingesting raw or undercooked poultry meat. Although poultry and other birds are not affected by the bacterium, other animals can be. Therefore it is possible for a person to aquire the infection from contact with infected stool of an ill cat or dog. This is what Campylobacter organisms look like through a microscope. (Image courtesy of the Centers for Disease Control and Prevention.)

Clostridium difficile is a bacterium commonly found in the intestinal tract but which, under the right circumstances such as after or during antibiotics therapy, can be the cause of enterocolitis. (Image courtesy of the Centers for Disease Control and Prevention.)

The esophagus, stomach, large and small intestine, aided by the liver, gallbladder and pancreas convert the nutritive components of food into energy and break down the non-nutritive components into waste to be excreted.

Food is swallowed and passes through the esophagus to the stomach, where the majority of digestion takes place.