FIG. 4.

Evolutionary scenarios. Serotypes, phenotypes, genotypes, critical events, and postulated intermediate form (circle) in three different scenarios leading to the five STEC 1 forms known to exist today (boxes). One asterisk indicates that the sequence of listed events is not known but is presumed to have occurred at different times during evolution. This result would obviate the need for postulated lineage B or C to produce such an organism. Two asterisks indicate that organisms in this box would not exist if lineage A exists.