Regional Differences in Attachment of Enteroadherent Escherichia coli Strain RDEC‐1 to Rabbit Intestine

Abstract

SummaryRDEC‐1 (serotype 015:NM) is an enteropathogenic Escherichia coli that adheres to mucosal epithelial cells in the ileum, cecum, and colon, but not in the jejunum, of rabbits during diarrheal illness. As RDEC‐1 can adhere to jejunal brush borders in vitro, rapid distal clearing of the enteropathogen from the upper gastrointestinal tract may explain the absence of in vivo adherence of RDEC‐1 to rabbit jejunum. To test this hypothesis, self‐filling blind loops (SFBL) were created in the jejunum of rabbits that were then inoculated with RDEC‐1 to determine if stasis would promote increased luminal colonization and increased mucosal attachment of RDEC‐1 in the proximal small intestine. Eight rabbits with SFBL and seven nonoperated littermates were inoculated with RDEC‐1 4 weeks after surgery. Semiquantitative estimation of fecal shedding of RDEC‐1 and the presence and severity of diarrhea were monitored for 7 days. Rabbits were then killed, and colonization of jejunum and ileum by anaerobic bacteria and luminal colonization of jejunum, ileum, and cecum by RDEC‐1 was quantitated. Mucosal adherence of RDEC‐1 to jejunum, ileum, and cecum was determined by Giemsa staining of intestinal sections obtained from rabbits with and without SFBL. In addition, brush border membranes (BBM) were prepared from blind loop jejunum, nonoperated jejunum, and ileum. In vitro adherence of RDEC‐1 to brush borders was quantitated under phase contrast microscopy. Maximal fecal shedding of RDEC‐1 began 3–4 days after infection in all rabbits, but diarrhea was more severe in rabbits with SFBL. As anticipated, the total number of anaerobic bacteria in jejunal blind loops (12.28 ± 2.01 log10 CFU/cm) and adjacent afferent segments (11.77 ± 0.88) was elevated, compared with levels in the jejunum of nonoperated rabbits (6.14 ± 1.76). Luminal colonization with RDEC‐1 developed in both jejunal SFBL (6.38 ± 0.80) and in adjacent jejunal segments only to the same degree as in the jejunum of nonoperated rabbits (5.27 ± 0.97). Despite stasis and luminal colonization of SFBL jejunum with RDEC‐1 (6.38 ± 0.80) in levels indistinguishable from those found in the ileum (6.43 ± 0.78), RDEC‐1 was not adherent to SFBL jejunum but was adherent to rabbit ileum. In vitro studies indicated that RDEC‐1 could adhere to BBM prepared from both non‐operated (6.0 ± 1.0 RDEC‐1/BBM) and SFBL jejunum (6.5 ± 1.8), as well as to ileal brush borders (8.0 ± 2.0). We conclude that although RDEC‐1 colonize the lumen of the upper jejunum during in vivo infection of rabbits, the organisms do not adhere to jejunal enterocytes even in a region of stasis such as the SFBL. Stasis was not sufficient to promote mucosal adherence of RDEC‐1, nor did the presence of anaerobic flora in the jejunum alter the intestinal mucosa in such a way as to promote enteroadherence of the pathogen. As RDEC‐1 could adhere to SFBL and normal jejunal brush borders in vitro, these studies suggest that factors other than intestinal transit prevent attachment of RDEC‐1 to enterocytes in the jejunum in vivo.