FIG. 4.

Cytotoxicity of wild-type and mutant holotoxins. Holotoxins or Stx1As, at the concentrations indicated, were incubated with Vero cells for 72 h. Cell viability was determined by microscopic analysis and expressed as a percentage. The datum points are the means ± the SE of one representative experiment. Holotoxins are indicated by shaded symbols, and Stx1As are indicated by open symbols as follows: wild type, • and ○; F226Y, ▴ and ▵; A231D, ▾ and ▿; G234E, ⧫ and ◊; A231D-G234E alone, ■ and □.