PRODUCTION OF A COMPLETE BINARY TOXIN (ACTIN-SPECIFIC ADP-RIBOSYLTRANSFERASE) BY CLOSTRIDIUM-DIFFICILE CD196

A Clostridium difficile isolate was found to produce an actin-specific ADP-ribosyltransferase (CDT) humologous to the enzymatic components o f Clostridium perfringens iota toxin and Clostridium spiroforme toxin (M. R. Popoff, E. J. Rubin, D. M. Gill, and P. Boquet, Infect. Immun. 56:2299-2306, 1988). The CDT locus from C. difficile CD196 was cloned and sequenced. It contained two genes (cdtA and cdtB) which display or ganizations and sequences similar to those of the iota toxin gene. The deduced enzymatic (CDTa) and binding (CDTb) components have 81 and 84 % identity, respectively, with the corresponding components of iota to xin. CDTa and CDTb induced actin cytoskeleton alterations similar to t hose caused by other clostridial binary toxins. The lower level of pro duction of binary toxin by CD196 than of iota toxin by C. perfringens was related to a lower transcript level, possibly due to a promoter re gion different from that of iota toxin genes. The cdtA and cdtB genes have been detected in 3 of 24 clinical isolates examined, and cdtB alo ne was found in 2 additional strains. One strain (in addition to CD196 ) was shown by Western blotting to produce CDTa and CDTb. These result s indicate that some C. difficile strains synthesize a binary toxin th at could be an additional virulence factor.