The present invention relates to immunogenic compositions comprising isolated Clostridium difficile CDTb. In particular the isolated Clostridium difficile CDTb protein has been mutated to modify pore forming ability, to modify heptamerisation ability, or is a truncated CDTb protein with the signal peptide and the prodomain removed and also the receptor binding domain removed and/or the CDTa binding domain removed. The invention also relates to fusion proteins comprising a CDTa protein and a CDTb protein. Vaccines comprising such immunogenic compositions and therapeutic uses of the same also form part of the invention.
