Pathophysiology of enteroaggregative Escherichia coli infection: an experimental model utilizing transmission electron microscopy

Abstract

-Context -Enteroaggregative Escherichia coli strains have been associated with persistent diarrhea in several developing countries. In vivo procedures with animal models as rat, rabbit and gnotobiotic piglets intestinal loops, in vitro assays with cellular lines like T84, Caco 2, HT29, HeLa e HEp-2 and in vitro organ culture with intestinal fragments have been applied to study these bacteria and their pathogenicity. Objectives -The present experimental research assessed the pathogenic interactions of three enteroaggregative Escherichia coli strains, using the in vitro organ culture, in order to observe and compare alterations in different regions of both, the ileal and the colonic mucosa. Methods -This study applied intestinal fragments from terminal ileum and colon that were excised from pediatric and adult patients that underwent colonoscopic procedures. Tissue was fixed for transmission electron microscopic study. Each bacterium was tested with three intestinal fragments for each region. Results -Enteroaggregative Escherichia coli strains colonized and provoked citotoxic effects in the ileal and colonic mucosa. Total or partial villi destruction, vacuolization of basal cytoplasm of the enterocytes, epithelium detachment, derangement of the structure and epithelial cell extrusion in ileal mucosa could explain the perpetuation of the diarrhea. Bacterial aggregates were seen in intestinal lumen associated with mucus and cellular debris and in the intercellular spaces of the destroyed epithelium, suggesting bacterial invasion that seemed to be secondary to the destruction of the tissue. Conclusions -Pathogenesis of persistent diarrhea should include alterations in the small bowel structures where the digestive-absorptive functions take place. In the colonic mucosa the inflammatory lesions could explain the occurrence of colitis.

Pathogenesis of Human Enterovirulent Bacteria: Lessons from Cultured, Fully Differentiated Human Colon Cancer Cell Lines

“…This IVOC system has been used mainly to study the mechanisms of virulence of ETEC (839), EPEC (840)(841)(842)(843)(844)(845)(846)(847)(848)(849)(850)(851), EHEC (852)(853)(854)(855)(856)(857), EAEC (507,858), and Salmonella (392) and the action of Stx toxins (641). Other IVOCs have been used for studies on C. jejuni (859), EPEC (692,860,861), EAEC (645,(862)(863)(864), and Shigella (865) pathogenesis. Moreover, IVOCs from colonic biopsy specimens from CD patients have been used to show the adhesion of AIEC (444,866).…”

Diarrheagenic Escherichia coli

“…Data from these in vitro , in vivo and ex vivo experiments strongly indicate that EAEC can bind to jejunal, ileal and colonic epithelium in the characteristic aggregative pattern, forming a strong biofilm in a mucus layer, followed by cytotoxic and proinflammatory effects 260, 266, 267, 268, 269, 270. Fragments from terminal ileum and colon excised from pediatric and adult patients were incubated with EAEC strains that were capable to colonize the ileal and colonic mucosa in the typical stacked-brick pattern over an augmented mucus layer 270 …”

Morphology of the Intestinal Barrier in Different Physiological and Pathological Conditions

“…Electron microscope observation showed that Enteroaggregative Escherichia coli strains caused total or partial villi destruction, vacuolization of basal cytoplasm of the enterocytes, epithelium detachment, derangement of the structure and epithelial cell extrusion in ileal mucosa. Bacterial aggregates associated with mucus and cellular debris was evident in the intestinal lumen and in the intercellular spaces of the destroyed epithelium, suggesting bacterial invasion which seemed to be secondary to the destruction of the tissue [19].…”