Purpose: This study aimed to investigate the influence of T3SS and surface polysaccharides of Escherichia coli O157:H7 and long polar fimbriae (Lpf) of E. coli O104:H4 on survival of the Shiga toxin-producing E. coli (STEC) on plant tissue.
Methods: Four week-old Arabidopsis thaliana (model plant) was dip-inoculated with STEC strains; E. coli O157:H7 EDL 933 wild-type and its isogenic T3SS-defective mutant, E. coli O157:H7 86-24 wild-type and its isogenic mutants (cellulose-deficient, colanic acid-deficient, and lipopolysaccharide (LPS)-truncated), and E. coli O104:H4 C3493 wild-type and Lpf-deficient mutants. Populations of each strain, expressed as a log CFU/g leaf tissue, on Arabidopsis plant were determined on day 0, 1, 3, and 5 postinoculation. Levels of plant defense response, based on expression of pathogenesis-related gene (PR1), was examined by reverse transcription quantitative PCR.
Results: The populations of wild-type E. coli O157:H7 and T3SS-defective mutant on Arabidopsis plants did not show a significant difference on day 1, 3, and 5 (P>0.05). The wild-type of E. coli O104:H4 and its corresponding Lpf mutants, similarly, showed no significant difference in the population at day 5 postinoculation (P>0.05). In regard to the influence of surface polysaccharides of E. coli O157:H7, however, wild-type strain survived better on Arabidopsis with two-fold lower expression of PR1 gene compared with colanic acid-deficient and LPS-truncated mutants (P<0.05).
Significance: This study demonstrated that different surface polysaccharides of STEC can trigger the plant defense response, thereby affecting the survival of the human pathogens on plants. The overall results provided a better understanding about the behavior of STEC on plants, which is helpful for designing intervention strategies for providing safe crops.