Figure 3

Cytopathic effect of recombinant toxins. Mouse colonic epithelial CT26 cells in a 96-well plate were untreated (A) or treated as following: 10 μl culture supernatant from pHis-TcdB-transformed B. megaterium without (B) or with (C) xylose induction; (D) 10 μl culture supernatant from pHis-SP-TcdB-transformed B. megaterium with xylose induction; (E) rTcdB (1 ng/ml); (F) native TcdB (1 ng/ml); (G) rTcdB (10 ng/ml); (H) native TcdB (10 ng/ml); (I) rTcdA (20 ng/ml); (J) native TcdA (20 ng/ml); (K) rTcdA (200 ng/ml); (L) native TcdA (200 ng/ml); (M) rTcdA (200 ng/ml) plus 1 μl/well of rabbit anti-TcdA serum; or (N) native TcdA (200 ng/ml) plus 1 μl/well of rabbit anti-TcdA serum. Cells were incubated overnight and the morphological changes were observed under a phase-contrast microscope.