The ecology of Escherichia coli

Although E. coli is primarily a commensal of mammals, and to a lesser extent birds, it can be isolated from a variety of host species as well as soil, sediments, and water. It has long been recognized that E. coli exhibits quite extensive substructuring and that the relative abundance of the most common phylo-groups varies with respect to host age and sex, host species, as well as geographical location. Strains belonging to some phylo-groups are much more frequently encountered in water samples than strains belonging to other phylo-groups. The extent to which strain survival in the external environment has determined the evolutionary origins of the various diarrheal pathotypes is unknown. There is a growing body of evidence that indicates commensal E. coli, like the diarrheal pathotypes, exhibits at some tissue specificity within the gastrointestinal tract. However, there is little evidence to suggest that commensal E. coli exhibit extensive host specificity as is the case with many of the diarrheal pathotypes.