Purified axial filaments from eight serotypes of Treponema hyodysenteriae and two nonpathogenic intestinal spirochaetes were characterized by SDS-PAGE and Western blotting. Axial filaments of all ten strains had similar SDS-PAGE profiles; five major axial filament polypeptides were identified, with molecular masses of 43.8, 38, 34.8, 32.8 and 29.4 kDa. Hyperimmune gnotobiotic pig serum raised against purified axial filaments of strain P 18A (serotype 4) cross-reacted with all other serotypes and with the non-pathogens, and convalescent serum taken from a pig with persistent swine dysentery also showed a strong response to the axial filament polypeptides. Hyperimmune gnotobiotic pig serum raised against axial filaments failed to agglutinate viable organisms and did not inhibit growth in vitro. Hence, the axial filaments of T. hyodysenteriae have been identified as major immunodominant antigens, although the role that antibodies to these antigens play in protection has yet to be established.

Outer envelopes of Treponema hyodysenteriae strains PI 8A and VS1 were prepared and characterized by SDS-PAGE. In Western blot analysis of eleven strains of T. hyodysenteriae and two intestinal non-pathogenic spirochaetes, polyclonal antiserum raised to the outer envelopes of strain P18A contained antibodies primarily to two polypeptides. A 45 kDa polypeptide was present in only two strains of T. hyodysenteriae, P 18A and MC52/80, whereas another antigen of 16 kDa was common to all eleven strains of T. hyodysenteriae but was not present in the two nonpathogens. Immunogold labelling of whole organisms suggested that the 16 kDa antigen was present on the surface of the spirochaetes. In in vitro tests the serum agglutinated and inhibited growth of only the T. hyodysenteriae strains, suggesting that antibodies to the 16 kDa antigen were responsible for these activities. Serum from a gnotobiotic pig infected with T. hyodysenteriae strain P18A had antibodies to the 16 kDa antigen alone and also possessed agglutinating and growth-inhibitory activities.

Twelve intestinal spirochete strains of porcine origin were characterized on the basis of their phenotypic properties, by multilocus enzyme electrophoresis, and by pathogenicity testing in gnotobiotic pigs. The spirochetes used included two strains of Serpulina hyodysenteriae (B204 and P18A), two strains of Serpulina innocens (B256 and 4/71), one strain from the proposed new genus and species "Anguillina coli" (P43/6/78), and seven non-S. hyodysenteriae strains recently isolated from United Kingdom pig herds with a history of nonspecific diarrhea and typhlocolitis. By multilocus enzyme electrophoresis, five of these were identified as S. innocens, one was identified as an unspecified Serpulina sp., and one was identified as "A. coli." S. hyodysenteriae B204 and P18A, "A. coli" P43/6/78 and 2/7, and three (22/7, P280/1, and 14/5) of the five S. innocens field isolates induced mucoid feces and typhlocolitis in gnotobiotic pigs. None of the other spirochetes produced clinical signs or large intestinal pathology in this model. The "A. coli" strains induced a more watery diarrhea, with lesions present more proximally in the large intestine, than did the other pathogenic spirochetes. S. innocens 22/7 was also tested for pathogenicity in hysterotomy-derived pigs that had previously been artificially colonized with a spirochete-free intestinal flora and shown to be susceptible to swine dysentery. Despite effective colonization, strain 22/7 did not produce any disease, nor was there any exacerbation of large intestinal pathology or clinical signs when pigs with an experimentally induced existing colitis caused by Yersinia pseudotuberculosis were superinfected with strain 22/7. Certain non-S. hyodysenteriae spirochetes are therefore capable of inducing disease in gnotobiotic pigs, but their role as primary or opportunistic pathogens in conventional pigs remains equivocal.

Summary. The haemolysin from a virulent strain of Treponerna hyodysenteriae was extracted and injected into ligated loops of the ileum and colon of germ-free pigs. It caused severe epithelial damage, especially to the differentiated cells at the tips of the villi in the ileum and the cells in the intercrypt zones of the colon; goblet cells were less affected. The changes in the colon were similar to those seen in natural cases of swine dysentery. The ligated loop offers a means of investigating pathogenic mechanisms and the mode of action of the toxin. This study demonstrated that the haemolysin was a potent cytotoxin for pig enterocytes, and a probable virulence determinant in swine dysentery.

Summary. The production of haemolysin from Treponema hyodysenteriae was increased by an improved culture method and by repeated incubation of spirochaetes suspended in a buffer containing RNA-core. Ion exchange chromatography on DEAE cellulose followed by gel filtration on Sephadex GlOO yielded purified haemolysin free from extraneous protein, as judged by silver-stained polyacrylamide gels. The mol. wt of the purified haemolysin, determined by gel filtration was 19 000, a value similar to that of streptolysin S, but much lower than that previously reported.