Purpose: The objective of this study was to determine the role of selected major surface structures of E. coli O157:H7 in adherence to biotic and abiotic surfaces.
Methods: A set of isogenic deletion mutants lacking major surface structures was generated. The wild type and the mutant strains were inoculated on fresh produce (spinach leaves) and glass surfaces, and the capability of bacteria to adhere to biotic and abiotic surfaces was assessed by adherence assays and fluorescent microscopy methods. The expression of the genes encoding for the cell surfaces proteins was determined following shifting cell cultures from 37°C to 25°C and 4°C by RT-qPCR.
Results: Most of the surface structure deficient strains bind to the spinach leaves and glass surface less strongly compared to the wild type strain. The reduction in adherence to spinach leaves was especially prominent in the cases of the flagellar filament structural protein (fliC) and outer membrane protein A (ompA) deletion mutants, which retained approximately 17% and 12%, respectively, of that of the wild type strain. The deletion of several other cell surfaces proteins, including curli, perosamine synthetase (per, an enzyme essential for the production of O antigen), long polar filament A (lpfA) and other filamental structures also led to reduced adherence to spinach leaves, but the effect was less significant. The upregulation of the expression of target genes upon temperature shift also underlines the importance of filamental structures in adaptation of E. coli to the new environment.
Significance: We conclude that pili, flagella and other filamental structures are important factors in the process of initial attachment and in the establishment of biofilms.