Plant Defense Response to Escherichia coli O157:H7 Cell Surface Structures Influences Survival of the Enteric Pathogen on Plant Surfaces

Introduction: Bacterial surface components such as curli, flagella, lipopolysaccharides, and exopolysaccharides have been shown to play an important role in the interactions between bacteria and plant surfaces.  It has been suggested that induction of plant defense responses by human enteric pathogens may influence their colonization on the plant.

Purpose: The objectives of this study were to investigate how E. coli O157:H7 cell surface structures influence the plant host defense responses and subsequently affects colonization or survival of the pathogen on plants.     

Methods: Arabidopsis thaliana ecotype Columbia (Col-0) wild-type and Arabidopsis BGL2-GUS transgenic plants were dip inoculated with E. coli O157:H7 strain ATCC 43895 and strain 86-24, and isogenic mutants lacking specific cell surface structure(s) at a concentration of approximately 10⁸ CFU/ml in water for 30 s.  At 0, 1, 3, and 5 days post-challenge wild-type Arabidopsis plants were harvested and the populations were determined by plating the homogenates on TSA supplemented with appropriate antibiotics.  At day 5 post inoculation GUS activities of BGL2-GUS transgenic plants were determined to monitor plant defense responses.

Results: On day 5 post inoculation, the population of E. coli O157:H7 43895 wild-type and flagella mutant on Arabidopsis wild-type plant was 5.05 and 6.53 CFU/g, respectively.  Plants inoculated with the 43895 wild-type strain showed more than a 2-fold increase in GUS activity compared with the 43895 flagella mutant. Curli-deficient E. coli O157:H7 86-24 strain (6.83 CFU/g) highly colonized wild-type Arabidopsis plants compared with the curli-producing 86-24 wild-type strain (5.76 CFU/g).  GUS activity of plants inoculated with the 86-24 curli mutant and 86-24 LPS mutant exhibited a 3-fold lower GUS activity compared with plants inoculated with the 86-24 wild-type strain. 

Significance: This study demonstrated that differences in bacterial cell surface structure of E. coli O157:H7 significantly influenced colonization through triggering differential plant defense responses.