Immunocytochemistry of the AfaE adhesin and AfaD invasin produced by pathogenic Escherichia coli strains during interaction of the bacteria with HeLa cells by high-resolution scanning electron microscopy.

We used a recent scanning electron microscope equipped with field emission gun and highly sensitive detectors to develop a fast and simple protocol for double immunogold staining using 10- and 15-nm gold particles. We used this approach to analyse the afimbrial adhesive sheath produced by pathogenic Escherichia coli interacting with the surface of epithelial cells. We demonstrated that AfaE adhesin and AfaD invasin were exposed at the bacterial surface during the interaction. This method could be easily and widely extended to the study of the early invasion process of many bacterial and viral pathogens, by immunocytochemical probing.