Experimental infection of newborn pigs with an attaching and effacing Escherichia coli O45:K"E65" strain

Abstract

The ability of a nonenterotoxigenic, K88-negative porcine Escherichia coli strain of serogroup O45:K"E65" to induce attaching-effacing lesions was investigated in newborn pigs. Typical attaching-effacing lesions, characterized by intimate adherence of bacteria to mature enterocyte brush borders with effacement of the microvilli, were observed on light and electron microscopy. Bacteria were also seen in intracytoplasmic vacuoles of mature enterocytes and, in areas of heavier colonization, in the lamina propria of the intestinal mucosa. A moderate inflammatory response with mild focal ulceration of the intestinal mucosa was observed. In a sequential study, we observed that the attaching-effacing lesions were well established in the duodenum, jejunum, and ileum at 12 h postinoculation but did not develop in the cecum and colon until 24 to 48 h postinoculation, although bacteria had colonized the latter areas as early as 12 h postinoculation. Initially, bacteria were very intimately attached, with an irregular arrangement on the enterocyte apical cell membrane, and subsequently reoriented to form a typical palisade arrangement with a narrow regular gap between the bacterial cell wall and the enterocyte apical cell membrane. This phenomenon of early intimate attachment of irregularly disposed bacteria has not been reported for human enteropathogenic attaching and effacing E. coli and could represent a new and different mechanism of attachment and effacement to intestinal epithelial cells.

Attaching-effacing Bacteria in Animals

“…Attaching-effacing Bacteria in Animals AE lesions have been reported in all regions of the gastrointestinal tract from the stomach to the rectum. In the small intestine, blunting, atrophy and fusion of villi accompany the changes described above (Moon et al, 1983;Peeters et al, 1984a;Moxley and Francis, 1986;Schoonderwoerd et al, 1988;Pearson et al, 1989Pearson et al, , 1999Iijima et al, 1990;Helie et al, 1991;Fagundes-Neto et al, 1995;Higgins et al, 1997;Gunning et al, 2001). Crypt hyperplasia is also reported in the small intestine (Ulshen and Rollo, 1980;Pospischil et al, 1987).…”

“…The numbers of such bacteria appear to be small relative to the surface population (Takeuchi et al, 1978;Peeters et al, 1984a;Helie et al, 1991). In some cases, bacteria were seen in the lamina propria (Helie et al, 1991;Wada et al, 1996a).…”

“…Intracytoplasmic bacteria (both in vacuoles and free within the cytoplasm) have been observed in AE lesions due to EPEC and EPEC-like organisms in human patients (Fagundes-Neto et al, 1995), rabbits (Takeuchi et al, 1978;Peeters et al, 1984a), pigs (Helie et al, 1991), dogs (Wada et al, 1996a) and cotton-top tamarins (Mansfield et al, 2001b). The numbers of such bacteria appear to be small relative to the surface population (Takeuchi et al, 1978;Peeters et al, 1984a;Helie et al, 1991). In some cases, bacteria were seen in the lamina propria (Helie et al, 1991;Wada et al, 1996a).…”

“…Descriptions of the histopathological appearance of intestines colonized by AE bacteria are consistent across species. These species include cattle (Hall et al, 1985;Moxley and Francis, 1986;Pospischil et al, 1987;Schoonderwoerd et al, 1988;Janke et al, 1989Janke et al, , 1990Pearson et al, 1989;Iijima et al, 1990), pigs (Helie et al, 1991;Neef et al, 1994;Higgins et al, 1997), rabbits (Polotsky et al, 1977;Peeters et al, 1984a), human beings (Ulshen and Rollo, 1980;Rothbaum et al, 1982), monkeys (Mansfield et al, 2001b) and poultry (Fukui et al, 1995). In general, bacteria adhere to enterocytes in an extensive or multifocal pattern and typically have a distinct, coccoid appearance (Janke et al, 1989).…”

“…At low magnification this gives a ragged, irregular, "scalloped" or "cobblestone" appearance to the mucosal surface (Moon et al, 1983;Hall et al, 1985;Janke et al, 1989;Pearson et al, 1989;Higgins et al, 1997;Mansfield et al, 2001b). Bacteria may be seen inside enterocytes, which are heavily colonized on their apical surface (Helie et al, 1991). An inflammatory infiltrate of variable intensity, typically neutrophilic but sometimes mixed, is often seen in the lamina propria.…”