Specific in situ Hybridization of the Intracellular Organism of Porcine Proliferative Enteropathy

The identity of the intracellular bacteria found in the enterocytes of pigs with proliferative enteropathy was investigated using specific DNA probes to various Campylobacter species and to a novel organism, ileal symbiont intracellularis. The ilea from pigs (Nos. 1–7) that were diagnosed by routine histopathology as having proliferative enteropathy were used. Diagnosis was made on the basis of proliferation of the enterocytes on hematoxylin and cosin-stained sections and the presence of large numbers of intracellular curved organisms on Warthin-Starry silver-stained sections. Four of these pigs (Nos. 1–4) had the chronic form of the disease, porcine intestinal adenomatosis, and three (Nos. 5–7) had the acute form, proliferative hemorrhagic enteropathy. An additional three normal pigs (Nos. 8–10) were obtained from three separate farms with no history of proliferative enteropathy. Frozen ileal sections were examined by in situ hybridization with DNA probes specific for ileal symbiont intracellularis and the three porcine intestinal Campylobacter species, C. coli, C. hyointestinalis, and C. mucosalis. In all seven pigs with either the intestinal adenomatosis or hemorrhagic enteropathy form of the disease, a DNA probe specific for ileal symbiont intracellularis hybridized to localized foci in the apical cytoplasm of ileal enterocytes. These hybridization sites corresponded to the location of intracellular bacteria in silver-stained sections of adjacent tissue. Sections from the three normal pigs tested with this probe and from all pigs tested with the Campylobacter species-specific DNA probes showed no specific hybridization reactions. The identity of the intracellular organism in these diseased pigs is ileal symbiont intracellularis.