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.