Purification and characterisation of two forms of toxin B produced by Clostridium difficile

Toxin B from Clostridium difficile was purified to homogeneity by gel filtration and high resolution ion exchange chromatography. Two forms of toxin B were found. Form 1 which seemed to consist of two identical subunits of 220-300 kDa; femtogram amounts of this toxin induced rounding of fibroblast cells. Form 2 contained subunits of 43 kDa and 105 kDa; the stoichiometric ratio probably being 4:1; picogram amounts were needed to induce rounding of fibroblast cells. Immunological studies suggested that both subunit types were antigenic and had epitopes which were identical with those of form 1.