Core-gene tree close-up on O157:H7 strains. The tree is a close-up of the O157:H7 clade from the core-gene tree presented in Figure 6. The names has been colored according to the three outbreaks described in . Blue strains represent the spinach outbreak, red strains represent the Taco Bell outbreak and the green strains represent the Taco John outbreak. Branch lengths have been modified to create the best visual output and thus have no value.