Molecular and ecological characterisation of Escherichia coli from plants

Meric, Guillaume (2011) Molecular and ecological characterisation of Escherichia coli from plants. Doctoral thesis, University of East Anglia.

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Escherichia coli is routinely isolated from vegetables and there is increasing evidence
that plants are a secondary reservoir for commensal and pathogenic strains, but the
ecological factors involved in the persistence of E. coli on plants are not clear. In this
thesis, a comparative study was undertaken combining phenotypic and phylogenetic
analyses of E. coli isolates from salads grown in the UK and the faeces of mammalian
hosts. In vitro phenotypic profiling revealed significant differences according to the
source of isolation: strains from plants were in the majority from phylogroup B1,
displayed lower siderophore production, greater motility, higher biofilm production,
and better growth on the aromatic compounds and sucrose. However, plant-associated
isolates reached lower growth yields on many carbon sources, including several
amino acids and common carbohydrates such as glucose and mannitol. The data
obtained indicate that in addition to lateral gene transfer, variation (regulation or
uptake) in core metabolic functions plays an important role in E. coli ecological
adaptation. When the discriminating phenotypes were combined to generate a plant
association index (PAi) to rank strains according to their potential to persist on plants,
a strong association between PAi and phylogeny was found, notably high levels in
phylogroup B1 and low levels in phylogroup B2 which could potentially constitute a
good predictor for host specialisation and generalisation in E. coli. As a more applied
and preliminary investigation, the question of how a strain with a medium level of
PAi (GMB30) can influence the resident microflora of field- and laboratory-grown
spinach was also addressed. Overall, this study shows that despite frequent acquisition
and loss of traits associated with nonhost environments, the E. coli phylogroups differ
substantially in their transmission ecology, and in the adaptation levels to their host.

Item Type: Thesis (Doctoral)
Faculty \ School: Faculty of Science > School of Biological Sciences
Depositing User: Users 2259 not found.
Date Deposited: 06 Mar 2014 11:43
Last Modified: 06 Mar 2014 11:43


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