Figure 2. Dose-response characteristics of antibiotic-induced expression of stx2::lacZ. Exponential-phase inocula were exposed to antibiotics for 4 h (white bars) or 24 h (black bars), and β-galactosidase activity was determined at the end of these periods. Fold-increase = Test activity (+ antibiotic) / control activity (- antibiotic). Note the difference in scale between upper and lower panels. *MICs refer to the antibiotic concentrations required to inhibit growth in the Bioscreen system, using the same inoculation pattern as in the antibiotic induction experiments. The values were cefuroxime 10 g/L, furazolidone 32 g/L, trimethoprim 0.6 g/L and ofloxacin 0.05 g/L.