Table 1. Cytotoxicity of purified native and recombinant TcdA and TcdB toxins.
Recombinant plasmids were transferred to the C. difficile production strain and expressed toxins purified from 8 l fermentations (Methods). The cytotoxic potencies of the recombinant wt toxins were found to be indistinguishable from native toxins purified from VPI 10463 (List Biologicals).
| Toxin | Genotype | IMR-90 EC50 (ng ml−1) | Fold reduction in cytotoxicity |
| Toxin A native | wtTcdA | 0.9 | 1.0 |
| Toxin A recombinant | wtTcdA | 1.0 | 1.1 |
| DM-TcdA | TcdA D285A/D287A | 12 900 | 14 000 |
| TM-TcdA | TcdA D285A/D287A/C700A | 8600 | 9300 |
| TM-TcdA formalin-treated | TcdA D285A/D287A/C700A | >100 000 | >100 000 |
| TM-TcdA antibody-treated | TcdA D285A/D287A/C700A | >100 000 | >100 000 |
| Toxin B native | wtTcdB | 0.009 | 1.0 |
| Toxin B recombinant | wtTcdB | 0.006 | 0.7 |
| DM-TcdB | TcdB D286A/D288A | 14 | 1600 |
| TM-TcdB | TcdB D286A/D288A/C698A | 74 | 8200 |
| TM-TcdB D270A/R273A/D461A/K463A | TcdB D286A/D288A/C698A/D270A/R273A/ D461A/K463A | 127 | 14 000 |
| TM-TcdB E970K/E976K | TcdB D286A/D288A/C698A/E970K/E976K | 10 000 | 1 100 000 |
| TM-TcdB formalin-treated | TcdB D286A/D288A/C698A | >100 000 | >10 000 000 |
| TM-TcdB antibody-treated | TcdB D286A/D288A/C698A | >100 000 | >10 000 000 |