Transcriptional induction of the STX2 gene in STEC strains O157:H7 and O104:H4 by various antibiotics. STEC strains O157:H7 and O104:H4 were inoculated into L-broth at a density of 1x108 bacteria/ml. The cultures were either left without antibiotics or treated immediately with the indicated n-folds of the MIC of the indicated antibiotics and incubated at 37°C under vigorous shaking. After 2 h, 200 μl of the bacterial suspensions were harvested to prepare total RNA and to determine by qRT-PCR the numbers of STX2-specific transcripts. Green or red columns highlight the values after treatment with the 1-fold or 4-fold MIC, respectively. This colour code is used throughout the manuscript. Shown are the means and standard errors of three independent experiments. Statistical significance is indicated by asterisks: * for p < 0.05.