TABLE 2.

Sensitivity of different cell lines to C. difficile toxins TcdA and TcdB^a

Cell line	Concn of toxin (ng/ml) required to cause 100% cell rounding		Fold difference
	TcdA	TcdB
Vero	4	0.0125	320
Caco-2	5.75	0.22	26
CCD-18Co	248	0.00098	253,725
T84	2.44	4.88	2

^aConfluent monolayers of the indicated cell lines were incubated for 24 h in serial dilutions of purified TcdA or TcdB. The cytopathic effects were determined by microscopic examination. The fold difference is the ratio of the concentration of TcdA divided by the concentration of TcdB (concentrations for 100% cell rounding).