Stool from mice infected with the most virulent strains that produced only Stx2 was ~10- to 100-fold more cytotoxic than from avirulent strain JH2012 on days 1 and 3 post-infection and 10-fold more cytotoxic than from the strain with delayed virulence, JH2013, on day 1 post-infection (Figure 2C). This evidence concerns the gene STX2 and infection.