Let us now consider the mechanisms of diarrheal disease caused by invasive bacterial pathogens. Invasive bacteria account for more than half of the mortality due to foodborne illness in the United States, yet we are only beginning to understand how they cause diarrhea . This lack of understanding contrasts with that for diarrhea caused by enterotoxigenic bacteria. The latter release soluble toxins into the intestinal lumen, thereby altering epithelial function without mucosal invasion. Examples include cholera and enterotoxigenic Escherichia coli, the latter being the major causative agent of traveler’s diarrhea . Therefore, we have initiated studies that seek to define the mechanisms of diarrhea produced by invasive bacteria, especially Salmonella typhimurium, which is prevalent in both developed and developing countries.
We first studied signaling events that occur rapidly when S typhimurium bacteria encounter the apical membrane of intestinal epithelial cells grown in culture. Interestingly, in light of the foregoing discussion, the bacteria cause a prompt, yet transient, activation of the EGF receptor . This occurs in a manner that is independent of bacterial invasion, as assessed by using mutant bacterial strains that lack the capacity to invade, yet can still bind to epithelial cells . This activation of the EGF receptor appears to be secondary to the bacterium’s ability to mobilize intracellular calcium, which might otherwise be expected to stimulate chloride secretion. Indeed, we have shown that the ability of Salmonella to cause early activation of the EGF receptor is responsible for limiting ongoing chloride secretion. Best quality drugs are waiting – buy viagra super active online to spend less time and money.