Recognition of the cellular beta1-chain integrin by the bacterial AfaD invasin is implicated in the internalization of afa-expressing pathogenic Escherichia coli strains.

Summary The afa operons from Escherichia coli associated with extra-intestinal and intestinal infections have been characterized and the AfaD protein has been shown to be involved in the low internalization of laboratory strains expressing the afa-3 operon. The aim of this study was to determine the role of the AfaD invasin during the interaction of pathogenic E. coli with epithelial cells. We show that AfaD is implicated in the entry of a clinical isolate into both HeLa and undifferentiated Caco-2 cells. Once in the cytoplasm of these cells, the bacteria formed inclusions in which they were able to survive for at least 72 h. Internaliza- tion assays using polystyrene beads coated with His 6 - tagged purified AfaD (rAfaD) demonstrated that this invasin mediates entry into cells derived from various tissues (intestine and urothelium) that are targets for afa -positive strains. Consistent with the previous observation that an antibody blockade involving anti- a 5 b 1 integrin abolishes bacterial internalization, we show here that the entry of rAfaD-coated beads was dependent on the production and accessibility of b 1 integrins on the cells. The AfaD proteins belong to a family of invasins that are at least 45% identical. Despite their differences, the recombinant rAfaD-III and rAfaD-VIII proteins both bound to b b b 1 integrins.