Abstract:
Escherichia coli is widely considered to not survive for extended periods outside the intestines of warm-blooded animals;
however, recent studies demonstrated that E. coli strains maintain populations in soil and water without any known fecal
contamination. The objective of this study was to investigate whether the niche partitioning of E. coli occurs between cattle
and their pasture. We attempted to clarify whether E. coli from bovine feces differs phenotypically and genotypically from
isolates maintaining a population in pasture soil over winter. Soil, bovine fecal, and run-off samples were collected before and
after the introduction of cattle to the pasture. Isolates (363) were genotyped by uidA and mutS sequences and phylogrouping,
and evaluated for curli formation (Rough, Dry, And Red, or RDAR). Three types of clusters emerged, viz. bovine-associated,
clusters devoid of cattle isolates and representing isolates endemic to the pasture environment, and clusters with both. All
isolates clustered with strains of E. coli sensu stricto, distinct from the cryptic species Clades I, III, IV, and V. Pasture soil
endemic and bovine fecal populations had very different phylogroup distributions, indicating niche partitioning. The soil
endemic population was largely comprised of phylogroup B1 and had a higher average RDAR score than other isolates. These
results indicate the existence of environmental E. coli strains that are phylogenetically distinct from bovine fecal isolates, and
that have the ability to maintain populations in the soil environment.
