Resistance of Escherichia coli to osmotically introduced complement component C9

Investigation into the action of osmotically introduced C9 in Escherichia coli (in the absence of any other complement components) revealed that C9 could inhibit inner membrane respiration and cause a decrease in the viability of cells that were normally complement sensitive. This effect is analogous to the loss of inner membrane function and viability due to the assembly of the C5b-9 complex on these cells. Complement-resistant cells showed no such inhibition of respiration or loss of viability when subjected to the osmotic introduction of C9. The reason for this failure of C9 to affect complement-resistant cells was explored to determine whether this resistance to C9 was due to an inability of proteins in general to be osmotically introduced into the complement-resistant cells. The protein toxins melittin and colicin E1 were showed to be able to kill these complement-resistant cells (as well as complement-sensitive cells) when osmotically introduced into the periplasm. Therefore, cellular resistance to osmotically introduced C9 is not due to an inability of proteins to be introduced into the cells and may be related to a mechanism of cellular resistance to the C5b-9 complex.