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theses

Previous studies have shown that human pathogens are able to colonize plants epiphytically and endophytically by utilizing similar mechanisms as phytopathogens. In addition, it has been suggested that colonization of plants by human pathogens induces plant defense responses, although some of their pathogenic mechanisms differ from those of phytopathogens. However, knowledge about the mechanism by which human pathogens colonize and persist on or in fruits and vegetables is limited compared to the research in plant pathogens. Also it is not well understood what factors are involved in intimate association of foodborne pathogens with plants and the plant response to enteric bacteria. To address these questions, we investigated whether Escherichia coli O157:H7 cell surface structures induce plant host defense responses and subsequently affect colonization or survival of the pathogen on plants. Also, the influence of growth medium or exposure conditions on bacterial cell surface structures, particularly in exopolysaccharides, was investigated, and subsequent impacts on plant defense responses and bacterial survival on plants were also examined. Among the pathogen associated molecular patterns (PAMPs), flagella made a substantial impact on survival of E. coli O157:H7 on the Arabidopsis plant. Curli were recognized by the Arabidopsis plant and induced plant defense responses. E. coli O157:H7 mutants lacking flagella or curli induced lower PR (pathogenesis-related) genes based on the weak β-glucuronidase (GUS) activity compared to flagella or curli positive E. coli O157:H7, resulting in increased survivals of those mutants on the plant. E. coli O157:H7 grown in Luria-Bertani (LB) broth supplemented with manure extracts showed a significant 58% increase in capsular polysaccharides (CPS) production as compared to cells grown in LB medium alone. Exposure of E. coli cells to soil and manure extracts also stimulated the CPS compared to the non-exposed control. Plants inoculated with E. coli O157:H7 with a greater amounts of CPS resulted in less inductions of PR genes compared to those with less CPS, contributed to the enhanced survivals on the Arabidopsis plant. Cell surface structures of E. coli O157:H7 have a significant impact on the induction of differential plant defense responses, thereby impacting survival of the pathogen on plants. Growth medium or exposure environment conditions showed a great impact on bacterial CPS, which enabled the human pathogen to persist longer on the plant by possibly evading plant defense responses.

ETD_4526

Ph.D.

Includes bibliographical references

Includes vita

by Seung-Wook Seo

http://hdl.rutgers.edu/1782.1/rucore10001600001.ETD.000068965

doi:10.7282/T30000NM

ETD doctoral

The author owns the copyright to this work.