Diffusely adherent Escherichia coli strains expressing Afa/Dr adhesins (Afa/Dr DAEC): hitherto unrecognized pathogens

Diffusely adherent Escherichia coli (DAEC) strains are currently considered to constitute a putative sixth group of diarrheagenic E. coli. However, on the basis of their diffuse adherence to HEp-2 and HeLa cells, the detection of afa/dra/daa-related operons encoding this adherence phenotype, and the mobilization of decay-accelerating factor, both commensal and pathogenic strains can be classified as Afa/Dr DAEC isolates. Furthermore, strains associated with diarrheal diseases and strains causing extra-intestinal infections can also be identified as Afa/Dr DAEC strains. Although several cell signaling events that occur after epithelial cells have been infected by Afa/Dr DAEC have been reported, the pathophysiological processes that allow intestinal and extra-intestinal infections to develop are not fully understood. This review focuses on the genetic organization of the afa/dra/daa-related operons and on the virulence factors that trigger cellular responses, some of which are deleterious for the host cells. Finally, this review suggests future lines of research that could help to elucidate these questions.