Comparison of Serpulina hyodysenteriae B78, the type strain of the species, with other S. hyodysenteriae strains using enteropathogenicity studies and restriction fragment length polymorphism analysis.

The enteropathogenicity of Serpulina hyodysenteriae B78, the type strain of the species, was compared with S. hyodysenteriae B204, a known pathogenic strain, in 7 week-old pigs. Clinical signs of swine dysentery were observed in 11/18 pigs (61.1%) inoculated with S. hyodysenteriae strain B204. However, in pigs inoculated with S. hyodysenteriae B78, only 1/21 (4.8%) of the pigs became infected. The 21 pigs inoculated with strain B78 included four pigs which received 5-fold higher numbers of S. hyodysenteriae B78 cells than were normally used in test inoculations. None of the four pigs became infected. Restriction fragment length polymorphism (RFLP) analysis, using a randomly cloned piece of S. hyodysenteriae B204 genomic DNA as the probe (pSRM5), was found to be useful in distinguishing S. hyodysenteriae strains. RFLP analysis confirmed that the one S. hyodysenteriae B78-inoculated pig that exhibited clinical signs of swine dysentery was infected with S. hyodysenteriae B78, and not by contamination with S. hyodysenteriae B204. These results indicate that S. hyodysenteriae B78 is only weakly pathogenic and should not be used in experimental infections of swine or in studies of virulence determinants where use of a pathogenic strain of S. hyodysenteriae would be crucial.