Application of a pig ligated intestinal loop model for early Lawsonia intracellularis infection

<p>Abstract</p> <p>Background</p> <p>Porcine proliferative enteropathy in pigs is caused by the obligate, intracellular bacterium <it>Lawsonia intracellularis</it>. <it>In vitro </it>studies have shown close bacterium-cell interaction followed by cellular uptake of the bacterium within 3 h post inoculation (PI). However, knowledge of the initial <it>in vivo </it>interaction between porcine intestinal epithelium and the bacterium is limited. The aims of the present study were to evaluate the usefulness of a ligated small intestinal loop model to study <it>L. intracellularis </it>infections and to obtain information on the very early <it>L. intracellularis</it>-enterocyte interactions.</p> <p>Methods</p> <p>A ligated small intestinal loop model using three different <it>L. intracellularis </it>inocula was applied to 10-11-week-old pigs. The inocula were 1) wild type bacteria derived from overnight incubation of <it>L. intracellularis </it>bacteria from spontaneous disease, 2) crude vaccine bacteria (Enterisol^®Ileitis Vet), and 3) vaccine bacteria propagated in cell culture. The bacteria-enterocyte interaction was visualised using immunohistochemistry on specimens derived 1, 3 and 6 h PI respectively.</p> <p>Results</p> <p>Although at a low level, close contact between bacteria and the enterocyte brush border including intracellular uptake of bacteria in mature enterocytes was seen at 3 and 6 h PI for the vaccine and the propagated vaccine inocula. Interaction between the wild-type bacteria and villus enterocytes was scarce and only seen at 6 h PI, where a few bacteria were found in close contact with the brush border.</p> <p>Conclusions</p> <p>The ligated intestinal loop model was useful with respect to maintaining an intact intestinal morphology for up to 6 h. Furthermore, the study demonstrated that <it>L. intracellularis </it>interacts with villus enterocytes within 3 to 6 h after inoculation into intestinal loops and that the bacterium, as shown for the vaccine bacteria, propagated as well as non-propagated, was able to invade mature enterocytes. Thus, the study demonstrates the early intestinal invasion of <it>L. intracellularis in vivo</it>.</p