Bacteria have developed mechanisms to communicate and compete with each other for limited environmental resources. Certain Escherichia coli , including uropathogenic strains, contain a bacterial growth-inhibition system that uses direct cell-to-cell contact. Inhibition is dependent upon the growth state and protein expression state of the inhibitory cell. Both a large cell-surface protein designated Contact-dependent inhibitor A (CdiA), and two-partner secretion family member, CdiB, are required for growth inhibition. Immunity to growth inhibition is conferred by a small immunity region adjacent to cdiA containing an open reading frame designated cdiI. Uropathogenic E. coli, however, do not appear to contain an immunity protein suggesting that these strains may be capable of autoinhibition. Colanic acid and K15 capsule as well as P and S pili confer resistance to contact-dependent growth inhibition (CDI) in a cdiI-independent manner. Notably, the PapG adhesin located at the P pilus tip is required for specific inhibition of CDI. Genetic analyses show that mutations in acrB, coding for an inner membrane multidrug efflux pump, confers complete resistance to contact-dependent growth inhibition. Disruption of the acrA and tolC genes, coding for additional components comprising a TolC-AcrA-AcrB multidrug efflux pump did not affect CDI, suggesting a separate role for AcrB in the CDI pathway. In this study a constructed contact-dependent autoinhibition system is also used to observe the effects of CDI on a single population of cells. By combining constitutively-expressed cdiAB with arabinose-inducible immunity, cdiI, growth inhibition is induced by withholding arabinose from the culture medium. Using this system CDI is observed to be a reversible, ATPase-independent process resulting from a reduction in proton motive force and septation defects in the cell. These results suggest that cells undergoing contact-dependent growth inhibition initiate a response pathway to low proton motive force, which has potentially important implications for the role of CDI in E. coli physiology and pathogenesis.