The presence of specific periplasmic proteins, such as TolA, TolB, TolC, or TonB, are required for translocation across the membrane.

Such resistant cells may suffer the lack of a key nutrient (such as iron or a B vitamin), but benefit by not being killed.

In his 1969 Nobel Laureate speech, Salvador E. Luria speculated that colicins could only be this toxic by causing a domino effect that destabilized the cell membrane.

[9] He was not entirely correct, but pore-forming colicins do depolarize the membrane and thus eliminate the energy source for the cell.

This suicidal production mechanism would appear to be very costly, except for the fact that it is regulated by the SOS response, which responds to significant DNA damage.

The Professor Kleanthous Research Group at the University of Oxford study colicins extensively as a model system for characterising and investigating protein-protein interactions and recognition.