Résumé
Entry of Listeria monocytogenes into cultured epithelial cells requires production of internalin, a protein with features characteristic of some Gram‐positive bacterial surface proteins, in particular an LPXTG motif preceding a hydrophobic sequence and a few basic residues at its C‐terminal end. By immunofluorescence and immunogold labelling, we show that in wild‐type L. monocytogenes , internalin is present on the cell surface and has a polarized distribution similar to that of ActA, another surface protein of L. monocytogenes involved in actin assembly. Through a genetic analysis, we establish that the C‐terminal region of internalin is necessary for cell‐surface association, and that although internalin is partially released in the culture medium, its location on the bacterial surface is required to promote entry. Finally, using a‘domain‐swapping’strategy ‐ replacement of the cell wall anchor of InIA by the membrane anchor of ActA ‐ we show that the reduced ability to adhere and enter cells of strains expressing InIA‐ActA correlates with a lower amount of surface‐exposed internalin. Taken together, these results suggest that internalin exposed on the bacterial surface mediates direct contact between the bacterium and the host cell.