Assessing the Activity of Bacterial Multidrug Efflux Pumps

Resistance to antibiotics in target bacterial populations has long complicated antibacterial chemotherapy. First described in the early 1980s (1 , 2 ), efflux mechanism of resistance, whereby the antibiotic is actively (i.e., in an energy-dependent fashion) pumped from the bacterial cell, are being described with increasing frequency in recent years. Initial examples of bacterial antibiotic efflux systems were agent-specific, providing for export of and resistance to single agents (e.g., tetracyclines, chloramphenicol, macrolides) (3 ). More recently, bacterial drug efflux systems of broad substrate specificity have been described (4 , 5 ). These systems are able to accommodate a wide variety of structurally unrelated antibiotics, contributing to intrinsic and acquired multiple antibiotic (multidrug) resistance.