Salmonella typhimurium is a gram negative bacteria. Commonly associated with disease, it is an organism that primarily is found in the intestinal tract. Since it requires a lower pH and a warm temperature to thrive, it will remain dormant in nature and only can reproduce inside of a host. Animals usually carry the bacteria, but it is not harmful to them for several reasons.
The Salmonella bacteria have a lipopolysaccharide membrane which is a protective measure against the environment. Inside the membrane, there is a substance called Lipid A which is a toxin in some circumstances. Animals have an enzyme in their intestines which breaks down the Lipid A and makes it harmless to them. Humans lack this enzyme and for this reason, contracting Salmonella can cause disease.
Humans contract the disease usually by the fecal-oral route. Animals who commonly carry salmonella in their digestive tract will expel fecal matter that contains the bacteria. Since animal waste is commonly used as manure, the bacteria can easily spread to produce or, very commonly, milk or eggs. Pasteurizing milk will prevent salmonella and cooking eggs will kill the bacteria as well. Eating raw eggs or unpasteurized milk puts individuals at greater risk for the disease. Also, produce should be thoroughly washed before eating to prevent any bacteria on the surface. These preventative measures will probably be sufficient. However, the disease can still be contracted from another individual or another food source.
Although this microorganism often triggers negative outcomes from a human’s perspective, the way it works is actually pretty amazing. The bacterial cells will seek out nonphagocytic cells and are able to manipulate themselves into the cells. The bacteria inside the cell can then safely live without being destroyed by other cells as well as the host cell.
When the bacteria enter the large intestine, they can cause gastroenteritis in humans. The bacterial cells will enter the epithelial cells of the intestine, damaging the cells. When the body’s defenses realize that the epithelial cells are being damaged, white blood cells will enter the intestine area, which causes problems for the digestive system, usually resulting in diarrhea. Although the disease causes discomfort, it is a self-limiting disease. The white blood cells are able to kill the bacteria and the intestinal system will expel them in human waste.