Role of multiple efflux pumps in Escherichia coli in indole expulsion.

Escherichia coli chromosome encodes several multidrug transporters. Despite their protective function against antibacterial agents, the specific physiological actions of these transporters are not fully understood. E. coli produces indole, a metabolite of tryptophan, under physiological conditions. Defined inactivation of the acrEF gene, the product of which is known as an energy-dependent multiple drug efflux pump, decreased indole excretion while reintroduction of the acrEF gene restored it. A DeltaacrEF mutant accumulated more intracellular indole than the parent. This mutant was more susceptible to the growth-inhibitory effect of indole than the parent. These results indicate that the AcrEF system plays a significant role in indole efflux.