Escherichia coli is adapted to the vertebrate intestinal tract. However, virtually every E. coli cell inevitably finds itself in an environmental external to the host, such as water, sediments and soil. There is an ever-growing body of evidence showing not all E. coli cell’s respond in the same manner to the host-environment transition, and the genetic background of the cell plays an important role in determining its fate. Our understanding of the nature of a cell’s response to the host-environment transition is lacking and the long-term goal of this study is to address this knowledge gap.
In order to accomplish this task it is necessary to identify E. coli strains that are over represented in environmental samples. To this end the genetic structure of E. coli populations in various water bodies in the Gold Coast and Sydney regions was determined at regular intervals of the course of a year. In total over 900 water samples were examined and over 10,000 E. coli isolates were characterised.
The results of this survey show the seven phylogenetic groups of E. coli vary greatly in the extent to which they are represented in water samples. Phylogroup B1 represented 49.7% of the isolates, followed by B2 (15%), A (13.3%), D (11.8%), E (8.4%), F (2%) and C (1.6%). There were significant differences in phylogroup distribution between the Sydney and Gold Coast regions, with A and B2 more common in Gold Coast samples, compared to D and E for Sydney. Additionally, spatial and temporal effects within a region were extensive, but the relative importance of these two factors varied with geographic region.
The study outcomes have significant implications for the use of E. coli as a water quality indicator, and enhance our understanding of how strains of the various phylogroups respond to the host environment transition.