Host cells rarely wish to admit bacterial invaders, butSalmonella has developed a clever way to get around this. It first injects a protein called SopE, which stimulates the host cell's outer membrane to form ruffles and take up the bacterium. Salmonellathen injects another protein, SptP, to reverse these effects, returning the cell to its normal state so that it will survive and can provide a comfortable home for the bacterium.
