The emergence and evolution of pathogenic Escherichia coli strains associated with diarrheal diseases
have become a topic of active investigation in recent years due to the emergence of more virulent strains and the
association of new serotypes with disease. Outbreak studies indicate that most patients with an intestinal E. coli
infection develop mild, uncomplicated diarrhea. However, a significant risk exists that infections caused by highly
virulent E. coli isolates, such as the enterohemorrhagic E. coli O157:H7, develop into serious and potentially lifethreatening
complications, such as hemolytic uremic syndrome. The relative contribution of recombination events in
the generation of new categories of pathogenic E. coli varies among the E. coli population, and it is represented by
the wide variety of mobile elements found in different diarrheal strains (e.g. pathogenicity islands, phages,
transposons, pathoadaptive mutations, etc). Understanding the population structure of pathogenic E. coli is
important, since it impacts the effectiveness of molecular epidemiological studies. Such studies are needed to
understand the increasingly recognized diversity of enterotoxigenic E. coli, a leading cause of pediatric and travelers’
diarrhea. In addition, factors underlying the emergence of enteroaggregative and atypical enteropathogenic E. coli
strains associated with persistent diarrhea are unknown. Horizontal transfer of genetic elements that affect virulence
of diarrheagenic E. coli strains and changes in global agricultural processes, as well as movement of humans and
animals, may contribute to the complex natural history of diarrheagenic E. coli.
