Escherichia coli in disguise: molecular origins of Shigella.

Shigella, which still stands as a genus with four species today, in reality belongs to the extremely diverse species Escherichia coli. There are several lineages of Shigella strains derived through independent acquisition of the pINV virulence plasmid. The chromosomally determined phenotypic properties of Shigella result from convergent evolution during niche adaptation, most due to loss of function, some from negative selection pressure.