Attaching and effacing adherence of Vero cytotoxin-producing Escherichia coli to rabbit intestinal epithelium in vivo

Abstract

Vero cytotoxin-producing Escherichia coli (VTEC) strains have been associated with sporadic cases and outbreaks of hemorrhagic colitis and with the hemolytic uremic syndrome in humans. Since adherence of enteric pathogens to epithelial surfaces is often a prerequisite for the subsequent delivery of bacterial enterotoxins and mucosal invasion, we evaluated intestinal adherence by 18 VTEC strains, which were of human origin and belonged to 10 distinct serotypes, 7 days after enteral challenge of rabbits. A total of 23 postweaning rabbits (body weight, 1 kg) were each fed 2 X 10(8) VTEC, and 5 rabbits were challenged with an equal number of fecal commensal E. coli strains as controls. Each rabbit was monitored daily for the development of diarrhea. At 7 days after infection the proximal jejunum, distal ileum, cecum, and proximal colon were removed from each rabbit and examined for the presence of adherent organisms under light microscopy, after Giemsa staining of Formalin-fixed secretions, and by transmission electron microscopy. Nonbloody diarrhea developed in 16 of 23 VTEC-infected rabbits in contrast to 0 of 5 infected with commensal E. coli strains (P less than 0.02). Organisms were adherent to surface epithelial cells in the ceca (20 of 23 rabbits), proximal colons (9 of 23), and distal ilea (6 of 23) of VTEC-infected rabbits. Intimate attaching and effacing binding of bacteria to intestinal epithelial cells, in regions where the normal microvillous membrane architecture had been disrupted, was observed under electron microscopy for VTEC of multiple serotypes. In contrast, no organisms were adherent to the jejuni. Adherence of organisms was not seen in any portion of the intestines of rabbits that were challenged with commensals. These findings indicate that multiple serotypes of VTEC demonstrate intimate attaching and effacing binding to rabbit enterocytes and colonocytes in vivo. In addition to bacterial binding in the ceca and colons, VTEC adhere to enterocytes in the distal small intestines of per orally infected postweaning rabbits.