CSTB and clostridium difficile infection: Ectopic constitutive expression (from the B. thailandensis rpsL promoter, PS12) of cognate bcpI genes, but not of the heterologous bcpIBtE264 gene, prevented BtΔbcpAIOB bacteria from growth inhibition by the chimeric strains, demonstrating that competition was indeed due to CDI and that the BcpI proteins tested here protect in an allele-specific manner (Fig. 2).