Exposure of Escherichia coli O157:H7 to soil, manure, or water influences its survival on plants and initiation of plant defense response.

This study evaluated whether growth medium or exposure conditions influence the production of capsular polysaccharides (CPS) by Escherichia coli O157:H7, and whether changes in CPS impact plant defense responses, consequently affecting survival on plants. E. coli O157:H7 grown in Luria-Bertani (LB) broth supplemented with manure extracts showed an approximately 58% increase in CPS production compared to cells grown in LB medium alone. Levels of CPS were significantly higher for E. coli O157:H7 cells exposed to soil or manure extracts as compared to the non-exposed LB cultured control. Arabidopsis thaliana plants expressing β-glucuronidase (GUS) under the control of the β-1,3-glucanase (BGL2) promoter were used to investigate whether E. coli O157:H7 induces defense-related gene expression. Plants inoculated with E. coli O157:H7 grown in LB containing manure extracts or cells exposed to manure extracts exhibited 3-fold and 2-fold lower GUS activity, respectively, suggesting a limited plant defense response compared to plants inoculated with cells grown in LB. On day 5 post inoculation the population of E. coli O157:H7 grown in LB supplemented with manure on plants was significantly greater than the population of E. coli O157:H7 grown in LB medium alone. E. coli O157:H7 cells exposed to soil or manure exhibited greater survival on plants compared to LB-grown E. coli O157:H7. The results of this study underscore the need to consider medium composition and cultural conditions when conducting crop challenge studies.