Purpose: The objective of this study was to investigate the influence of E. coli O157:H7 extracellular polysaccharides (cellulose, colanic acid, and lipopolysaccharide) on survival/colonization on plants.
Methods: Arabidopsis thaliana ecotype Columbia (Col-0) and Romaine lettuce were used in bacterial colonization experiments to compare survival trends on a plant model and produce commodity, respectively. Four week-old Arabidopsis plants and lettuce plants were dip-inoculated with wild-type E. coli O157:H7 strain 86-24 and its corresponding mutants (cellulose-deficient; ΔyhjN, colanic acid-deficient; ΔwcaD, and truncated LPS; ΔwaaI). Initial populations on day 0 were approximately 106 CFU/g leaf tissue. At days 1, 3, and 5 post-inoculation, three plants for each treatment were harvested and E. coli O157:H7 populations determined by plating plant homogenates onto Tryptic Soy Agar supplemented with appropriate antibiotics. Extracellular polysaccharide production of each strain was quantified using the hot phenol-water extraction method.
Results: On day 5 post-inoculation, the populations of colanic acid-deficient (2.79 log CFU/g) and LPS truncated (2.59 log CFU/g) mutants on Arabidopsis were significantly (P < 0.05) lower than the population of the wild-type strain (3.84 log CFU/g). Wild-type E. coli O157:H7 survived better on both Arabidopsis and lettuce than colanic acid-deficient and LPS truncated mutants at day 1 and 5 post-inoculation. The wild-type strain produced significantly greater (P< 0.05) amounts of extracellular polysaccharide than the colanic acid and LPS mutants.
Significance: This study demonstrates that E. coli O157:H7 polysaccharides colanic acid and LPS may impact survival of the pathogen on plants depending on the amount of extracellular polysaccharide produced.