Cytotoxic activity of E. coli expressing GtxA. (A) β-haemolytic activity of E. coli ER2566 grown on LB-agar with 5% bovine blood and 0.1 mM IPTG, incubated at 30 °C. T1SS: + or − indicates the presence or absence of plasmid pLG575 which expresses the E. coli T1SS-components HlyB and HlyD. RTX = amino acids 931–2026 of GtxA, N-term = amino acids 1–949 of GtxA. (B) Liquid haemolysis assay and LDH cytotoxicity assay with E. coli ER2566/pLG575 expressing different versions of GtxA.