FIG 8 .

StxB decreases the cytotoxicity of Stx produced by bacteria internalized by Tetrahymena cells. Tetrahymena cells were cocultured with MG1655 (recA)::λcI857/pStx and either 2 µg/ml BSA or StxB for 30 min at 30°C, uninternalized bacteria were removed by centrifugation, and the bacterium-containing Tetrahymena cells were incubated at 42°C as described in Materials and Methods. The Tetrahymena cells were enumerated subsequent to washing and again after incubation at 42°C. At the start of the incubation, Tetrahymena cells were present at approximately 10⁴/ml. Data are presented as the number of live Tetrahymena cells after incubation relative to the number of live Tetrahymena cells at the start of incubation. Error bars represent standard deviations from three or more independent experiments, with each experiment comprising a minimum of three individual measurements.