Enteropathogenic Escherichia coli (EPEC) contact secretion system. (Left) An enterocyte is shown with a microvillus border and a delicate supporting cytoskeleton. (Middle) An EPEC has attached to the cell surface by binding of the bundle-forming pili to receptors on the host cell surface. A type III secretion system apparatus has been inserted into the cell and is exporting secretion proteins (Esps) into the cytoplasm. One of these is the receptor for intimin. (Right) The intimin receptor has been inserted below the host cell membrane and is now mediating tight binding to the surface. The other Esps have disrupted multiple cellular functions, including the structure of the cytoskeleton. Cytoskeleton elements have been concentrated to form a pedestal cradling the EPEC (Figure 33–5). Bfp, bundle-forming pili.
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