Association of Serpulina hyodysenteriae with the colonic mucosa in experimental swine dysentery studied by fluorescent in situ hybridization

The localization of Serpulina hyodysenteriae in experimental swine dysenter y was studied by fluorescent in situ hybridization (FISH) using an oligonuc leotide probe targeting the 23S rRNA of S. hyodysenteriae. Nine 8-week-old pigs were challenged. Seven of the pigs were intragastrically dosed with 1x 10(9) cfu S. hyodysenteriae for 3 consecutive days, whereas two pigs were i nfected by contact. Six non-challenged pigs served as negative controls. Th e challenged pigs developed clinical swine dysentery from 8 to 14 days post infection with typical gross lesions. By FISH S. hyodysenteriae cells in hu ge numbers were found colonizing the mucus layer, the luminal epithelium an d the crypts of the large intestinal mucosa. The orientation of the spiroch aetes to the epithelium appeared to be random. Spirochaetes in clusters or as single cells were invading the epithelium and were occasionally detected in the adjacent lamina propria. The distribution of spirochaetes in the mu cosa provides further evidence that S. hyodysenteriae is intimately associa ted with the mucus layer and the epithelium in a random pattern. Furthermor e, the results demonstrate the applicability of FISH for specific detection of S. hyodysenteriae cells in clusters or as single cells in formalin-fixe d tissue samples.