These data suggest that during co-culture on solid medium, both strains participate in CDI, i.e., each strain attempts to inhibit the other (and possibly themselves), presumably by delivering toxic BcpA-CT into the cytoplasm of neighboring bacteria (however, autoinhibition does not occur due to the presence of the cognate immunity BcpI protein in ‘self’ bacteria). This evidence concerns the gene CSTB and clostridium difficile infection.