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How Do Salmonella Bacteria Cause Disease(s)?
The majority of Salmonella infections are due to ingestion of food or water, although direct contact with animals has become more common as a source of the organisms to cause infection. In people with normal gastrointestinal tracts and immune systems, researchers have estimated that about 1 million to 1 billion S. spp need to be ingested to cause infection, because normal human stomach acid can kill large numbers of these bacteria. If some bacteria reach the intestine, the organisms can attach to intestinal cells where S. spp toxins (cytotoxin and enterotoxin) can damage and kill cells. The intestinal cell damage results in the inability of the body to normally retain and adsorb fluids, so diarrhea results. In some people, the diarrhea can cause serious dehydration. However, the majority of S. spp-caused infections are then eventually eliminated by the person's immune defenses. Some S. spp are not eliminated; these bacteria survive the initial immune response by living inside cells (macrophages) of the immune system. The bacteria can sometimes spread to the blood (bacteremia). Some S. spp (for example, S. typhi) can also enter the gallbladder and remain there. The patient can recover from the disease but still sheds bacteria through the gallbladder secretions (bile) into the feces. This person thus becomes a carrier of S. spp and potentially can infect many others, especially if the person lives in unsanitary conditions or works in the food-processing industry.
Medically Reviewed by a Doctor on 12/23/2014
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