Category Archives: Diarrhea - Part 2

Pathogenesis of infectious diarrhea: GUT PHYSIOLOGY Part 8

Non-histotoxic Salmonella species: Non-histotoxic Salmonella species are an example of a pathogen that causes shortening of whole villi. Here, the picture, as observed in the rabbit ileal loop model, is totally different from that described for histotoxic Salmonella species. Bacteria enter via brush borders, and bacteria-laden cells are shed. There is no evidence of a rapid initial cleavage of tight junctions. The time scale of … Continue reading

Pathogenesis of infectious diarrhea: GUT PHYSIOLOGY Part 7

EAEC and DAEC: In comparison with the previously discussed E coli pathotypes, the pathogenesis of EAEC and DAEC infections are much less well understood. The characteristic histopathological feature induced by EAEC is the aggregation of bacteria entrapped within a mucous gel, accompanied, not surprisingly, by pitted goblet cells. In volunteer studies, diarrhea was predominantly mucoid. Genes encoding EAEC adhesins and EAST1 have been identified on … Continue reading

Pathogenesis of infectious diarrhea: GUT PHYSIOLOGY Part 6

EHEC: Since the early 1980s, EHEC has become a cause celebre with E coli 0157:H7 — a familiar household fear-inducing term. There are striking similarities between EPEC and EHEC. The most obvious similarity is the ability to form the intimate type of adhesion pedestal; the A/E lesion is readily demonstrable in conventional and gnotobi-otic pigs, infant rabbits and cultured cells, but not in humans because … Continue reading

Pathogenesis of infectious diarrhea: GUT PHYSIOLOGY Part 5

EPEC: Like ETEC, EPEC is essentially a pathogen of the small intestine. In the case of EPEC, and to a lesser extent EHEC, a similar situation exists to that described above for V cholerae. There has been a recent explosion of new molecular biological data; an appreciation of the biological significance follows. EPEC was the first serotype of E coli to be incriminated as a … Continue reading

Pathogenesis of infectious diarrhea: GUT PHYSIOLOGY Part 4

ETEC: ETEC are the most common cause of diarrhea in children in developing countries and in travellers to these areas, and an important pathogen of weanling animals. Clinically, disease can range in severity from mild self-limiting to severe life-threatening cholera-like diarrhea. The pathogenesis of ETEC infection is largely explicable in terms of two important virulence attributes: the ability to adhere to epithelial cell surfaces and … Continue reading

Pathogenesis of infectious diarrhea: GUT PHYSIOLOGY Part 3

Vibrio cholerae: V cholerae colonizes the upper small intestine by adhering to epithelial cells. Despite being arguably the most studied pathogen over the past three decades, the basis of V cholerae pathogenicity and the detailed mechanisms underlying the dramatic diarrheal secretion induced by this organism are still not fully understood. Recently, spectacular advances have been made in the molecular biology of V cholerae. Chromosomal DNA … Continue reading

Pathogenesis of infectious diarrhea: GUT PHYSIOLOGY Part 2

Villus tips and crypts are regarded as the anatomical sites of physiological absorption and secretion, respectively. Fluid transport is a bidirectional process in the healthy animal, with net absorption in health and net secretion in disease. The proximal small intestine is relatively leaky; in contrast, the terminal ileum and the colon are powerfully absorptive organs. The balance between absorption and secretion is poised at different … Continue reading

Pathogenesis of infectious diarrhea: GUT PHYSIOLOGY Part 1

One of the main functions of the gut is the selective active inward transport of ions and nutrient solutes that is followed by the passive movement of water. Highly simplified schematic representations of a small intestinal villus and of fluid uptake and physiological secretion are shown in Figures 1 and 2. The driving force is sodium/potassium ATPase situated in the basolateral membrane of enterocytes, which … Continue reading

Pathogenesis of infectious diarrhea

It is difficult, indeed unwise, to engage in meaningful discussion on the pathogenesis of infectious diarrhea without first considering the basic nature of the systems that, when perturbed, give rise to the pathophysiological state of diarrhea. It is also true that, in some cases (eg, diarrhea caused by enteropathogenic Escherichia coli [EPEC]), a great deal is known about the detailed molecular biology of initial attachment and the … Continue reading