Proteolytic activity of Clostridium difficile.

Ten isolates of Clostridium difficile expressing different degrees of toxigenicity and virulence in an animal model were assayed for the production of proteolytic enzymes by various methods. All strains demonstrated some activity in one or more of the assay systems. There was no direct correlation between toxigenic status and enzyme production. However, those strains known to be highly virulent in a hamster model were the most proteolytic. The most commonly detected enzyme was cell associated, and its substrate specificity suggested it was a trypsin-like enzyme. Initial purification of the enzyme from strain VPI 10463 gave a 10% yield with a 14-fold increase in purity. Inhibition studies on this preparation indicated that the enzyme was a thiol protease. The enzyme has pH and temperature optima of 7.5 and 37 degrees C, respectively. These characteristics suggest that the enzyme is more related to clostripain, the thiol clostridio-peptidase of C. histolyticum, than to trypsin. Whilst the role of this enzyme remains unclear, it is possible that it may be a contributory factor in the virulence of the organism as described for other clostridial infections.