Plant Science

Diversity of Escherichia coli isolated from a barley trial with organic supplements

E. coli is generally considered to be a mammal-adapted organism that only persists transiently outside the host. When detected in soil or water samples, the assumption is that this is evidence of faecal contamination. However, E. coli is adaptable and is present in a wide range of environmental conditions. In a study undertaken with pathologists at the James Hutton Institute, we investigated the diversity of E. coli from a barley field trial treated with two bulky organic soil amendments, municipal compost and bovine slurry. Soil and plant tissue samples were collected at different times of year under different irrigation regimes and tested for the presence of E. coli. Pathogenic isolates of E. coli were detected in soil samples and barley root and grain samples. Phylogenetic network analyses of alignments based on DNA sequences obtained from these samples found that E. coli isolates from the same source tended to be more closely related than isolates from different sources. This observation indicates genetic adaptation of some E. coli and supports the idea that E. coli can exist as a natural part of the soil microflora, rather than just being the transient contaminants transmitted from slurry. This work highlights the drawbacks of using E. coli as a faecal indicator species, as isolates were widespread and diverse, reinforcing the view that some are a natural part of the microflora in agricultural systems.

colonisation of spinach root Epiphytic colonisation of Spinach root (magenta) by E. coli O157:H7 Sakai (green)

Further details from: Adrian Roberts and Graham Horgan

Article date 2015

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