Molecular model of multidrug efflux pumps (blue) expelling antibiotics. They are expelling ciprofloxacin (yellow), chloramphenicol (violet) and ampicillin (red) from inside the bacterium. Multidrug efflux pumps are cell membrane proteins that actively transport unwanted, toxic substances out of cells. In this case, the transport protein is the CmeB efflux pump from the Campylobacter jejuni bacterium. Infections arising from multidrug-resistant bacteria are spreading rapidly throughout the world and threaten to become untreatable. Research into the intrinsic activity of efflux pumps and how to inhibit them, could help combat antibiotic resistance.