Porcine proliferative enteropathy in pigs is caused by the obligate, intracellular bacterium Lawsonia
intracellularis. In vitro 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 in vivo 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 L. intracellularis infections
and to obtain information on the very early L. intracellularis-enterocyte interactions.
A ligated small intestinal loop model using three different L. intracellularis inocula was applied to 10-
11-week-old pigs. The inocula were 1) wild type bacteria derived from overnight incubation of L.
intracellularis 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.
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.
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 L. intracellularis 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 L. intracellularis in vivo.
This is an Open Access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/2.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.