Molecular and ecological characterisation of Escherichia coli from plants

Abstract 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.

Name dc:type.qualificationname

phd

Level dc:type.qualificationlevel

doctoral

Grantor dc:publisher.institution

University of East Anglia

Year dc:date.issued

2011

Author dc:creator

• Meric, Guillaume

Language dc:language

en