Several inbred strains of mice in closed breeding colonies were found to have spiral-shaped bacteria associated with active, chronic hepatitis. A new species of , was isolated from the infected livers of some strains of mice. Other strains of mice were colonised with in the caecum and colon, but not the liver. Filter-sterilised supernatant fluid from five strains of was tested in a mouse liver cell line (ATCC no. CCL 9.1) for cytotoxic activity. All strains produced a toxic factor causing morphological changes in the cells at dilutions up to 1 in 1000. Toxicity was observed after exposure to the supernatant fluid for 48-72 h. Other spp. that also produced the cytopathic effect (CPE) in the liver cell line were and one strain of and did not cause CPE in the liver cells. The soluble factor was stable at 4C for up to 3 months. It was also stable at 56C for 30 min, but was inactivated by boiling for 15 min. It was inactivated by incubation with trypsin. A partially purified preparation of the cytotoxin had a mol. wt of 100000 and did not have urease activity. The cytotoxin produced by did not cause vacuole formation in HeLa cells.


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