The invention relates to a gene isolated from E. coli, dep, which confers resistance to the antibacterial activity of 4,5-dihydroxy-2-cyclopenten-1-one (DHCP). The invention further relates to the putative protein encoded by dep, which is a hydrophobic, transmembrane efflux protein specific for DHCP. The invention further relates to plasmids containing the dep gene, and to bacterial cells expressing dep. Furthermore, the invention provides applications for use in conferring resistance to antibacterial activity in organisms. The dep gene can be used to identify compounds which inhibit the efflux activity responsible for the resistance to DHCP or to compounds which are functionally equivalent to DHCP.