Purification and characterisation of two forms of toxin B produced by Clostridium difficile

Dithiothreitol generates an activated 250,000 mol. wt form of Clostridium difficile toxin B

The potent cytotoxin of Clostridium difficile, toxin B, is internalized by endocytosis and activated intracellularly by an unidentified mechanism. Here it is shown that dithiothreitol treatment of toxin B resulted in (1) a mol. wt of 250,000 which is the smallest species of this toxin shown to be cytotoxic; (2) an increased endpoint titre; and (3) translocation of plasma membrane-bound toxin across the membrane at pH 4.5. Treatment with dithiothreitol can thus mimic intracellular activation of the toxin. Radiolabelling of highly purified toxin with retained activity, as well as the 32 N-terminal amino acids and the amino acid composition, is also presented.

Sensitivity in culture of epithelial cells from rhesus monkey kidney and human colon carcinoma to toxins A and B from Clostridium difficile

The effect of toxins A and B from Clostridium difficile on human colon carcinoma cells (HT-29, epithelial), rhesus monkey kidney cells (MA-104, epithelial) and green monkey kidney cells (VERO, fibroblast) was studied. Both toxins caused rounding of HT-29 cells and rounding with projections remaining attached to the substrate in MA-104 and VERO cells; however, the sensitivity to each toxin varies considerably. Toxin A was detected in ng by VERO, pg by HT-29 and fractions of pg by MA-104 cells; for toxin B, pg were detected by VERO, ng by MA-104 and micrograms by HT-29 cells. HT-29 cells were grown with galactose to allow their differentiation to enterocytes, and their sensitivity to the toxins during the process was studied. At early stages, the sensitivity to both toxins was similar, and as the differentiation proceeded, the response to both toxins decreased continuously, and after 16 days no evident morphological effect was observed, even with micrograms amounts of either toxin. In contrast to all cell lines reported to date, HT-29 and MA-104 epithelial cells are exquisitely sensitive to toxin A and less responsive to toxin B. The rounding of HT-29 by these toxins depends on the degree of differentiation of the cell.

Degradation of 2-phosphoglycerate by cytotoxin B of Clostridium difficile

Cytotoxin B of C. difficile was highly purified by selective ammonium sulfate precipitation, Biogel A5m chromatography, phenyl boronate hydrophobic interaction chromatography and ultracentrifugation. The final cytotoxic product had a specific activity of 7.8 X 10(8) units/mg protein and showed a single protein band with an estimated molecular weight of 163,000 when subjected to SDS-PAGE. Immunoelectrophoresis of the final product showed a single precipitin arc. The addition of cytotoxin B to imidazole-HCl buffer (pH 7.4) containing MgSO4, KCl and the substrate 2-phosphoglycerate resulted in the formation of phosphoenolpyruvate as demonstrated by spectrophotometric analysis. Phosphoglycerate conversion was absent when the cytotoxin was heat-inactivated of reacted with specific antitoxin prior to assay.

Production, purification and characterization of Clostridium difficile toxic proteins different from toxin A and from toxin B

The purification and characterization of three new proteins called C1, C2, and C3 from Clostridium difficile are described. Their estimated molecular mass were about 350 (C1), 270 (C2) and 140 (C3) kDa, consisting of subunits of 39 (C1), 43 (C2) and 41 (C3) kDa, respectively. Immunodiffusion revealed that the three proteins contained similar but not identical antigenic determinants to toxin A. Each protein induced a cytotonic effect on hamster ovaric cells; the combined proteins, had a specific activity on cells 5-times higher than that of toxin A. In rat intestinal loops, they induced a clear fluid secretion, while toxin A elicited a haemorrhagic fluid response. The cytotonic activities of all three proteins were abolished by antiserum against toxin A, while antiserum against toxin B inhibited only the activity of the 270 kDa protein. In contrast to toxin A, the cytotoxicity of the three proteins was inactivated by trypsin. Thus, the chemical, antigenic and biological properties of these proteins differed from those of toxin A and toxin B.