ABSTRACT

Consumption of fresh and fresh-cut fruits and vegetables contaminated with Escherichia coli O157:H7 has resulted in hundreds of cases of illness and, in some instances, death. In this study, the influence of cell surface structures of E. coli O157:H7, such as flagella, curli fimbriae, lipopolysaccharides, or exopolysaccharides, on plant defense responses and on survival or colonization on the plant was investigated. The population of the E. coli O157:H7 ATCC 43895 wild-type strain was significantly lower on wild-type Arabidopsis plants than that of the 43895 flagellum-deficient mutant. The population of the E. coli O157:H7 43895 flagellum mutant was greater on both wild-type and npr1-1 mutant (nonexpressor of pathogenesis-related [PR] genes) plants and resulted in less PR gene induction, estimated based on a weak β-glucuronidase (GUS) signal, than did the 43895 wild-type strain. These results suggest that the flagella, among the other pathogen-associated molecular patterns (PAMPs), made a substantial contribution to the induction of plant defense response and contributed to the decreased numbers of the E. coli O157:H7 ATCC 43895 wild-type strain on the wild-type Arabidopsis plant. A curli-deficient E. coli O157:H7 86-24 strain survived better on wild-type Arabidopsis plants than the curli-producing wild-type 86-24 strain did. The curli-deficient E. coli O157:H7 86-24 strain exhibited a GUS signal at a level substantially lower than that of the curli-producing wild-type strain. Curli were recognized by plant defense systems, consequently affecting bacterial survival. The cell surface structures of E. coli O157:H7 have a significant impact on the induction of differential plant defense responses, thereby impacting persistence or survival of the pathogen on plants.