Human intestinal spirochetes are distinct from Serpulina hyodysenteriae

Twenty-nine intestinal spirochetes isolated from Australian aboriginal children and six strains from Italian adults (HRM1, -2, -4, -5, -7, and -14) were genetically examined at 15 enzyme loci by using multilocus enzyme electrophoresis. Results were compared with those previously obtained for 188 porcine intestinal spirochetes. DNA from human strain HRM7 and porcine strain Serpulina hyodysenteriae P18A were also radioactively labeled and hybridized with DNA from 12 other human and porcine intestinal spirochetes. Both the multilocus enzyme electrophoresis and hybridization techniques demonstrated that the human spirochetes were not S. hyodysenteriae. They belonged to another distinct genetic group of spirochetes that included P43/6/78, the bacterium recovered from the first recorded case of porcine intestinal spirochetosis. Bacteria in this distinct group also differed from Serpulina spp. in possessing only four, five, or occasionally six axial filaments, being slightly thinner, and having more pointed ends. These findings add further weight to the possibility that human intestinal spirochetes may act as enteric pathogens.