Differential Binding of Escherichia coli O157:H7 to Alfalfa, Human Epithelial Cells, and Plastic Is Mediated by a Variety of Surface Structures

Abstract

Escherichia coli O157:H7 carried on plant surfaces, including alfalfa sprouts, has been implicated in food poisoning and outbreaks of disease in the United States. Adhesion to cell surfaces is a key component for bacterial establishment and colonization on many types of surfaces. Several E. coli O157:H7 surface proteins are thought to be important for adhesion and/or biofilm formation. Therefore, we examined whether mutations in several genes encoding potential adhesins and regulators of adherence have an effect on bacterial binding to plants and also examined the role of these genes during adhesion to Caco-2 cells and during biofilm formation on plastic in vitro. The genes tested included those encoding adhesins (cah, aidA1, and ompA) and mediators of hyperadherence (tdcA, yidE, waaI, and cadA) and those associated with fimbria formation (csgA, csgD, and lpfD2). The introduction of some of these genes (cah, aidA1, and csg loci) into an E. coli K-12 strain markedly increased its ability to bind to alfalfa sprouts and seed coats. The addition of more than one of these genes did not show an additive effect. In contrast, deletion of one or more of these genes in a strain of E. coli O157:H7 did not affect its ability to bind to alfalfa. Only the absence of the ompA gene had a significant effect on binding, and the plant-bacterium interaction was markedly reduced in a tdcA ompA double mutant. In contrast, the E. coli O157:H7 ompA and tdcA ompA mutant strains were only slightly affected in adhesion to Caco-2 cells and during biofilm formation. These findings suggest that some adhesins alone are sufficient to promote binding to alfalfa and that they may exist in E. coli O157:H7 as redundant systems, allowing it to compensate for the loss of one or more of these systems. Binding to the three types of surfaces appeared to be mediated by overlapping but distinct sets of genes. The only gene which appeared to be irreplaceable for binding to plant surfaces was ompA.

Genome-Wide Transposon Mutagenesis Reveals a Role for pO157 Genes in Biofilm Development in Escherichia coli O157:H7 EDL933

“…These studies uncovered several new genes that are involved in biofilm formation. Our approach was not complete, however, as we also missed some genes already shown to be involved in biofilm formation in E. coli O157:H7, such as csgD, ompA, and cadA (58). This is because our screen was not saturating.…”

“…Because of this complexity, the process of biofilm formation and its regulation is poorly understood. Previous studies in E. coli O157:H7 have focused on individual genes and the specific genetic pathways that are responsible for biofilm formation (10,51,58,60). In contrast, few studies have focused on studying genetic factors that control E. coli O157:H7 biofilm formation on a global scale, although studies of this type have been performed with other bacterial pathogens (43,47,59).…”

“…Early studies have shown that some strains of E. coli O157:H7 form biofilms on both abiotic and biotic surfaces outside the host (15,51,58). Biofilms are exopolymeric matrixenclosed bacterial populations that are firmly adherent to each other and/or to surfaces (9).…”

Deciphering the Roles of Outer Membrane Protein A Extracellular Loops in the Pathogenesis of Escherichia coli K1 Meningitis

“…Enterohemorrhagic E. coli of serotype O157:H7 utilizes OmpA in adhering to HeLa epithelial cells and Caco-2 colonic epithelial cells (46). OmpA also appears to be critical in adherence to plant surfaces, as an ompA mutant of E. coli O157 did not colonize alfalfa bean sprouts (47). In addition, OmpA, together with the Hek protein, has been shown to be critical for the invasion of colonic epithelial cells by meningitic E. coli (48).…”

Molecular Mechanisms That Mediate Colonization of Shiga Toxin-Producing Escherichia coli Strains

“…Interestingly, no changes in the ability of prototype EHEC strain 86-24, compared to that of the double mutant strain, to adhere to Caco-2 cells, alfalfa sprouts, and seed coats were observed (89). These studies indicated that Cah plays a role in bacterial autoaggregation, but not in adherence of STEC to cells.…”