Pathogenesis and evolution of virulence in enteropathogenic and enterohemorrhagic Escherichia coli

Pathotypes and pathogenic clonesPathogenic forms of E. coli associated with human and animal diseases are remarkably diverse.Certain pathogenic strains cause enteric diseases ranging in symptoms from cholera-like diarrhea to severe dysentery; other E. coli may colonize the urinary tract, resulting in cystitis or pyelonephritis, or may cause other extraintestinal infections, such as septicemia and meningitis.In discussing the diversity of pathogenic forms of this versatile species, we distinguish between an isolate's pathotype, a classification of E. coli into groups that have a similar mode of pathogenesis and cause clinically similar forms of disease, and the pathogenic clone, bacteria of a genetic lineage within a bacterial species that share similarities because of recent descent from a common ancestral cell.There are at least eight recognized pathotypes of E. coli (Table 1) but many more distinct pathogenic clones (see Figure 1).Bacteria of the same pathogenic clone represent a monophyletic branch of an evolutionary tree and typically carry many of the same mobile genetic elements, including those that determine virulence.Early evidence for the clonal nature of pathogenic E. coli was seen in the repeated recovery of identical serotypes and biotypes from separate outbreaks of disease.