(Patho-)Genomics of Escherichia coli.

Escherichia coli represents a versatile and diverse enterobacterial species which can be subdivided into (i) nonpathogenic, commensal, (ii) intestinal pathogenic and (iii) extraintestinal pathogenic strains. This classification is mainly based on the presence or absence of DNA regions which are frequently associated with certain pathotypes. In most cases, this genetic information has been horizontally acquired and belongs to the flexible E. coli genome, such as plasmids, bacteriophages and genomic islands. These genomic regions contribute to the rapid evolution of E. coli variants as they are frequently subject to rearrangements, excision and transfer as well as further acquisition of additional DNA thus contributing to the creation of new (pathogenic) variants. Genetic diversity and genome plasticity of E. coli has been underestimated. The accumulating amount of sequence information generated in the era of "genomics" helps to increase our understanding of factors and mechanisms that are involved in diversification of this bacterial species as well as in those that may direct host specificity.