PMNs & Salmonella

Salmonella is a genus of bacteria that are common in the intestines of many reptiles, mammals and birds. Some salmonella bacteria can cause illness in humans, and salmonella are a frequent cause of food-borne infections.

Identification

• Salmonella enterica serovar Typhimurium (S. typhi) is a salmonella bacterium and the pathogen responsible for typhoid fever. S. typhi manages to make its way through the intestinal lining and invade the bloodstream, one of the reasons it's able to cause such serious illness. In response to S. typhi infection, cells in the intestinal lining secrete proteins such as interleukin 8. These chemical messengers, or chemokines, summon white blood cells such as polymorphonuclear leukocytes, or PMNs, to the scene.

Function

• The chemokines secreted by cells of the intestinal lining in response to infection cause inflammation, a common feature of S. typhi infections. As PMNs arrive, they migrate through the lining into the intestine, together with water and electrolytes. Various researchers have investigated the mechanisms whereby S. typhi can induce PMN migration into the small intestine; according to a 2008 study in the journal Infection and Immunity, S. typhi activates a pathway that leads to secretion of a chemokine called HXA3 by intestinal cells. HXA3 secretion appears to be essential for PMN migration into the intestine.

Features

• PMNs play an essential role in the body's defense against infection with salmonella bacteria. According to research cited in a 1998 study in Proceedings of the National Academy of Sciences, mice deficient in neutrophils--a type of PMN--are far more susceptible to a variety of pathogens including salmonella bacteria. PMNs, moreover, kill salmonella very efficiently in vitro (outside a living organism in a test tube or petri dish), in contrast to macrophages, another type of white blood cell.