Shigellosis: From Disease Symptoms to Molecular and Cellular Pathogenesis

Enteric bacterial pathogens may be divided into two pathovars: The noninvasive pathovar, exemplified by Vibrio cholerae and enterotoxigenic Escherichia coli (ETEC), cause disease by adhering to the apical side of the small intestinal epithelium and by secreting enterotoxins, thereby causing massive water and electrolyte secretion. Likewise, enteropathogenic E. coli (EPEC) and enterohemorrhagic E. coli (EHEC) colonize and partially destroy the epithelium. EHEC may even cause bloody diarrhea due to the production of Shiga-like toxins. However, in spite of significant epithelial alterations, these bacteria are not significantly invasive and the syndrome they cause is still dominated by watery diarrhea. In the case of Salmonella typhi infection, the intestinal phase of the invasive process may lead to limited symptoms, but crossing of the epithelial barrier allows the microorganisms to enter a septicemic phase that causes the systemic symptoms and complications characteristic of typhoid fever. In the case of Shigella , the invasive process remains localized to the colonic and rectal mucosa, thereby causing major inflammatory destruction that accounts for a dysenteric syndrome, thus the name bacillary dysentery. In many cases, however, shigellosis causes only a watery diarrhea similar to that observed with noninvasive pathogens.