The influence of ecological factors on the distribution and the genetic structure of Escherichia coli

This review focuses on recent data concerning the ecological factors that determine the distribution of Escherichia coli and the genetic structures of naturally occurring E. coli populations. It summarizes some of the older literature concerning the dynamics of E. coli populations within a host and poses some questions that arise from our more recently acquired understanding of the factors affecting the genetic structures of E. coli populations. Multilocus enzyme electrophoresis (MLEE) studies indicate that E. coli, relative to other members of the family Enterobacteriaceae, exhibits a moderate degree of genetic diversity. The existence of subspecific structure in E. coli has for the most part been determined by largely neutral in its effects on the fitness of a strain. The consequences for E. coli of the transition between its primary and secondary habitats are of considerable practical significance for water quality assessment and disease transmission. E. coli causes a significant fraction of human bacterial disease and is responsible for two main types of disease in humans and domestic animals: diarrheal disease and extraintestinal infections. The observed distribution of strains from the different E. coli genetic groups indicates that they have different life history tactics and ecological niches. A and B1 strains appear to be generalists, as they can be recovered from any vertebrate group. Group B2 and D strains appear to be more specialized, as they are largely restricted to endothermic vertebrates.