Pathogenic diversity of Escherichia coli and the emergence of 'exotic' islands in the gene stream

Escherichia coli is a highly adaptive bacterial species that is both a member of the commensal intestinal flora and a versatile pathogen associated with numerous types of intestinal and systemic infections in humans and other animals. The spectrum of diseases caused by E. coli is due to the acquisition of specific virulence genes harbored on plasmids, bacteriophages, or within distinct DNA segments termed pathogenicity islands (PAIs) that are absent from the genomes of commensal E. coli strains. PAIs are likely to have been transferred horizontally and may have integrated into the E. coli chromosome through bacteriophage or plasmid integration or transposition. The contribution of intergenic inheritance to the adaptation and evolution of E. coli, types of PAIs associated with different groups of pathogenic E. coli and approaches to identify unique sequence islands (USIs), some of which might confer pathogenicity, in E. coli and other bacteria are presented.