Isolithocholic acid at 0.01 % does not inhibit spore germination and outgrowth of CF5 and M120, but it significantly inhibits at the higher concentration (0.1 %). Isolithocholic acid (0.00003 %) prevents growth of CD196, M68, CF5, 630, and BI9 and significant decreases strains CF5, BI9, M120, and 630 in toxin activity. Isolithocholic acid (0.0003 %) makes that all strains displays a significant decrease in toxin activity, except for R20291 and M120.