Efflux (microbiology)

Active efflux is a mechanism responsible for moving compounds, like neurotransmitters, toxic substances, and antibiotics, out of the cell; this is considered to be a vital part of xenobiotic metabolism. This mechanism is important in medicine as it can contribute to bacterial antibiotic resistance.

Efflux systems function via an energy-dependent mechanism (active transport) to pump out unwanted toxic substances through specific efflux pumps. Some efflux systems are drug-specific, whereas others may accommodate multiple drugs, and thus contribute to bacterial multidrug resistance (MDR).

Efflux pumps are proteinaceous transporters localized in the cytoplasmic membrane of all kinds of cells. They are active transporters, meaning that they require a source of chemical energy to perform their function. Some are primary active transporters utilizing adenosine triphosphate hydrolysis as a source of energy, whereas others are secondary active transporters (uniporters, symporters, or antiporters) in which transport is coupled to an electrochemical potential difference created by pumping hydrogen or sodium ions from or to the outside of the cell.
Bacterial efflux transporters are classified into five major superfamilies, based on their amino acid sequence and the energy source used to export their substrates:

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