Variant toxin B and a functional toxin A produced by Clostridium difficileC34

A particular property of Clostridium difficile strain C34 is an insertion o f approximately 2 kb in the tcdA-C34 gene that does not hinder expression o f a fully active TcdA-C34 molecule. Intoxication with TcdA-C34 induced all arborized appearance in eukaryotic cells (D-type cytopathic effect); intoxi cation with TcdB-C34 induced a spindle-like appearance of cells (S-type cyt opathic effect). Inactivation of GTPases with purified toxins revealed that Rho. Rac, Cdc42, and Rap are substrates of Tcd.A-C34. The variant cytotoxi n TcdB-C34 inactivated Rho, Rac, Cdc42, Rap, Ral. and R-Ras. Hence, this is the first 'S-type' cytotoxin which inactivates both Rho and R-Ras, and is coexpressed with a 'D-type' enterotoxin. Our results support the hypothesis that R-Ras is a key GTPase related to the S-type cytopathic effect and sug gest that induction of a S-type cytopathic effect dominates induction of th e D-type cytopathic effect. (C) 2001 Federation of European Microbiological Societies. published by Elsevier Science B,V. All rights: reserved.