Cytotoxicity of Bacillus piliformis.

Seven isolates of B. piliformis, the agent of Tyzzer's disease, obtained from various host species, were examined for cytotoxic activity by incubating culture filtrates on BRL 3A rat-hepatocyte and 3T3 mouse-fibroblast cell lines. One isolate exhibited cytopathic effects on BRL 3A cells, but not on 3T3 cells. Three other isolates were strongly cytotoxic for 3T3 cells but only slightly so for BRL 3A cells. The remaining three isolates showed no cytotoxicity for either cell line. The cytotoxic products were greater than 100 kDa in mol. wt, thermolabile, and partly destroyed by trypsin treatment. The data show that some B. piliformis isolates produce cytotoxic proteins, which may contribute to the pathogenesis of Tyzzer's disease.