Bacterial Multidrug Efflux Pumps Serve Other Functions

Antibiotic efflux is one of several resistance mechanisms that are found in bacterial pathogens. Members of the resistance-nodulation-division (RND) family of antimicrobial exporters are particular noteworthy owing to the breadth of antimicrobials that these multidrug pumps accommodate. Found generally in gram-negative bacteria, where they are highly conserved, RND family members are almost always chromosomally encoded. RND pumps typically function as tripartite systems, with the cytoplasmic membrane (CM) RND component working with an outer membrane-spanning channel-forming protein, the outer membrane factor, and a periplasmic component, the membrane fusion protein, that links the membrane components (Fig. 1).