LIGHT-MICROSCOPIC AND ULTRASTRUCTURAL-CHANGES IN THE CECA OF CHICKS INOCULATED WITH HUMAN AND CANINE SERPULINA-PILOSICOLI

Light microscopic and ultrastructural changes were observed in chicks challenged with North American Serpulina pilosicoli, a weakly beta-hem olytic intestinal spirochete (WBHIS) associated with human and canine intestinal spirochetosis. Chicks in control groups received trypticase soy broth or canine Serpulina innocens. The birds were necropsied at weekly intervals, and the ceca were processed for bacteriologic and pa thologic examinations. No WBHIS were isolated from the ceca of chicks in the control groups, but WBHIS with genotypes similar to the parent isolates were isolated from the ceca of chicks inoculated with human a nd canine S. pilosicoli. Gross examination revealed no significant cha nges in the ceca of chicks at any time postinoculation. Light microsco pic examination revealed no spirochetal attachment in the ceca of chic ks in control groups. In contrast, focal to diffuse thickening of the brush border of the surface epithelium along with dilation of the cryp t lumina and mild focal lamina propria heterophil infiltration were pr esent in the ceca of chicks inoculated with human and canine S. pilosi coli. Scanning electron microscopic examination revealed focal to conf luent spirochetal attachment mainly in the furrow region at the periph ery of the crypt units. Transmission electron microscopic examination revealed spirochetes attached to the brush border of the cecal epithel ium, causing effacement of the microvilli and disruption of the termin al web microfilaments. The cecal epithelium of chicks inoculated with the canine S. pilosicoli also had caplike elevations of the apical mem brane at the point of attachment of the spirochetes together with larg e numbers of vesicles in the cytoplasm immediately beneath the termina l web and evidence of spirochetal invasion beyond the mucosal barrier. The changes observed suggested that the mechanism of attachment of hu man and canine S. pilosicoli to the cecal epithelium of chicks was ana logous to but different from that described previously for other attac hing and effacing gastroenteric bacterial pathogens of human beings an d animals.