Conclusions and Perspectives for the Future

During the past decade an increasing incidence of C. difficile disease has been evident worldwide. This bacterium is now recognized as a major nosocomial pathogen in industrialized parts of the world (Lyerly and Wilkins, 1995). The pseudomembranous colitis caused by C. difficile was early recognized as a toxin disease, i.e., all symptoms can be evoked by the toxins. Understanding the disease thus requires an understanding of the toxins. 

Our knowledge of the molecular toxicology of C. difficile has been considerably improved as the enzymatic mode of action of the toxins have been identified. This knowledge also has the potential to help in answering a whole array of questions related to the functions of small G-proteins in cells. However, a large number of obvious questions remain both concerning the toxins per se, and their actions on single cells and in the intestine. 

One intriguing point is the significant differences in cytotoxic and enterotoxic potencies between toxins A and B. What determines these differences Could the difference in cytotoxic potency simply reflect a difference in the affinity of the toxins for their cellular substrates Preliminary observations in our laboratory suggest that ToxA, in gluco-sylation assays in vitro, using either cell lysates or recombinant Rho, is 

Obviously the C. difficile toxins will become extremely useful tools for further studies of how the Rho subfamily proteins control the ACTSK, as well as aspects of cell proliferation in different types of cells (Olson et al., 1995). These toxins will be easier to use for manipulation of small GTPases than the exoenzyme C3 from C. bofulinum, because they are internalized into cells and are more potent. Their drawback compared with C3 is that they attack more than one target protein. Preparation of mutant toxins, fragments of toxins or hybrid toxins which discriminate between various GTPase targets might solve this problem and allow sophisticated studies of the cellular cross-talk between small GTPases (see further discussion in Chapters 10 and 15). 

We are grateful to Drs Ove Lundgren, Christoph von Eichel-Streiber, Patrice Boquet, and Alberto Alape Giron for stimulating discussions and helpful suggestions. Studies from the authors laboratory have been sponsored by the Swedish Medical Research Council (16X-05969) and Magnus Bergvalls Stiftelse. 

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