Ecology, Stress Response and Regulation of Virulence Genes in Escherichia coli

  • Author / Creator
    Yuan Fang
  • The genetic structure of Escherichia coli is diverse in virulence genes that are required for disease pathogenesis. Stress factors presented in nature, agricultural and food production shape the population structure and drive the acquisition of virulence and resistance genes. Shiga toxin producing E. coli (STEC) is a severe foodborne pathogen and acquired the Shiga toxin gene (stx) by phage lysogenization. The expression and transmission of stx are induced and regulated by stress factors. This research aimed to investigate the effect of ecological factors on the genetic variation and regulation of virulence genes in STEC.
    The phylogeny and the correlation between virulence and stress resistance genes were analyzed with 13,717 E. coli genomes to unravel the determinants that manipulate the genetic structure. The dynamic distribution of virulence and stress resistance genes suggested that the evolution of pathogenic E. coli evolved by the acquisition of virulence and stress resistance genes through horizontal gene transfer. Ecological factors contribute to shape the genetic structure by the selective maintenance of resistance mechanisms and virulence factors, which are beneficial for host-and niche-adaptation. Remarkably, acid resistance mediated by urease activity was correlated to gastrointestinal pathogenic E. coli, which reflects the adaptation to commensal habitats.
    To further understand the effect of environmental factors on the regulation of virulence genes, the expression, regulation and transfer of stx at abiotic stress conditions were explored. Hydrogen peroxide and organic acids used as antimicrobials in the food industry induced the expression of stx. Moreover, stx was differentially expressed at different stress conditions and in different genetic backgrounds. Oxidative stress induced the expression of stx and production of phage through the up-regulation of the RecA-dependent SOS stress response required for DNA repairs. Dehydration results in the generation of reactive oxygen species and induces the oxidative stress in the dehydrated cells. This study demonstrated that drying process resulted in the oxidation of the membrane lipids, and expression of stx in STEC. Moreover, the expression of Stx prophage in STEC that survived on dry seeds resulted in the transfer of stx to non-pathogenic E. coli during seeds germination. The contamination of STEC in low water activity foods compromises food safety by the transmission of virulence genes. In conclusion, this study improves the understanding of the effect of abiotic stress on the E. coli population structure and regulation of stx, which drives the genetic variation and virulence recombination in the ecological systems.

  • Subjects / Keywords
  • Graduation date
    Fall 2019
  • Type of Item
  • Degree
    Doctor of Philosophy
  • DOI
  • License
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