STX2 and infection: Host cells were infected in parallel with a ΔespZ mutant, a ΔespZ ΔescN mutant (which lacks an ATPase essential for T3SS activity), or a ΔespZ Δstx1 Δstx2 mutant (ΔΔstx [a mutant that does not produce Stx1 or Stx2]) or were mock infected, and the number of host cells present after 1 or 5 days of infection was determined (Fig. S1B).