Evolution of STEC virulence: Insights from the antipredator activities of Shiga toxin producing E. coli.

•E. coli O157:H7 from cows kill amoebae more efficiently than those from humans.•Recently evolved STEC O157:H7 kill amoebae less efficiently than progenitor clades.•Efficient amoebae killing is associated with the expression of Stx2c.•Q21-like antitermination proteins control Stx2c production in progenitor STEC.•Thus changes in Stx-encoding phage impact the virulence of STEC strains.