Molecular Epidemiology and Population Genetics of Extraintestinal Pathogenic Escherichia coli

Abstract

The strains of E. coli that cause such extraintestinal infection, in whatever host species, have long been recognized to differ, collectively, from those that colonize the intestinal tract or cause diarrhea in members of the same species. Such strains have been the subject of considerable study in an effort to better understand their distinguishing features, virulence mechanisms, host and syndrome range, evolutionary origins, reservoirs, and transmission pathways. This has led to the creation of various taxonomic categories and commensals. Such labels imply that the special ability of these strains to cause extraintestinal disease is their raison d'etre. Several broad generalizations can be made regarding the distribution of virulence factors among individual extraintestinal pathogenic E. coli (ExPEC) strains. First, ExPEC strains typically express representatives of multiple different functional categories of virulence factors. Second, ExPEC strains commonly display multiple representatives of a particular functional class of virulence factors. Third, different ExPEC strains exhibit radically different combinations of virulence factors, evidence that multiple E. coli genotypes can cause extraintestinal virulence. An important aspect of virulence genes, aside from presence/absence and expression, is point mutations. In contrast, pulsed-field gel electrophoresis (PFGE) analysis, which is relatively insensitive to broad phylogenetic relationships, provides resolution down to the level of individual clones within the larger clonal groups. Better understandings of ExPEC strains’ pathogenetic mechanisms, fecal reservoirs, transmission pathways, antimicrobial resistance development, and evolutionary origins are needed to guide the development of effective preventive measures against these important opportunistic pathogens.