Results of principal component analysis (PCA). Distances between data points represent the similarities between strains. Each STEC O157:H7 genotype corresponds to a color, as shown below. Lineage I, Q933, stx2a, SBI 3, tir(255T), non-clade 8 strains; Lineage I/II, Q933, stx2a, SBI 1, tir(255A), clade 8 strains; Lineage I/II, Q933, stx2a, SBI 1, tir(255T), clade 8 strains; Lineage I/II, Q933, stx2a+c, SBI 1, tir(255T), clade 8 strains; Lineage I/II, Q933, stx2c, SBI 1, tir(255T), clade 8 strains; Lineage I/II, Q21, stx2a+c, SBI 1, tir(255T), clade 8 strains; Lineage I/II, Q21, stx2c, SBI 1, tir(255T), clade 8 strains; Lineage I/II, Q21, stx2c, SBI 6, tir(255T), clade 8 strains; Lineage I/II, Q21, stx2c, SBI 6, tir(255T), non-clade 8 strains; Lineage I/II, Q21, stx2c, SBI 21, tir(255T), clade 8 strains; Lineage I/II, Q933+Q21, stx2a+c, SBI 1, tir(255T), non-clade 8 strains; Lineage I/II, Q933+Q21, stx2a+c, SBI 1, tir(255T), clade 8 strains; Lineage II, Q21, stx2c, SBI 5, tir(255A), non-clade 8 strains; Lineage II, Q21, stx2a+c, SBI 5, tir(255A), non-clade 8 strains; Lineage II, Q21, stx2a, SBI 1, tir(255A), non-clade 8 strains.