FIG 2.
Cytotoxic activity of supernatants of STEC and stx2dact-expressing C. rodentium strain. Strains O157:H7 EDL933, C. rodentium ϕstx2dact, and O104:H4 11-02027 were grown at 37°C in the presence of the indicated antibiotics. Supernatants of the cultures were withdrawn and cleared from bacteria by centrifugation. Bacteria-free supernatant of the O157:H7 EDL933 (A) or the O104:H4 11-02027 (C) culture was added to VeroB4 cells, and that of the C. rodentium ϕstx2dact culture was added to LLC-PK1 cells (B). After incubation for 72 h, XTT solution was added to PBS-washed cells for 2 h. Cells treated with 0.01% Triton X-100 were used as the positive (dead) control, while untreated cells were used as the negative (live) control. After incubation, the absorbance of the samples was determined at 475 nm and the cell viability of untreated cells was set to 100%. Shown are the mean values (±SEM) of three independent experiments performed in quadruplicate in comparison to the untreated control. Statistical analysis was performed via unpaired Mann-Whitney test (*, P < 0.05; **, P < 0.01; ***, P < 0.001), with all treated groups compared to the untreated control.